Fix pause to cancel probe goroutine; add Robot Framework integration tests

Pause semantics
- PauseBackend now cancels the probe goroutine so no HTTP/TCP/ICMP
  traffic is sent while the backend is paused. Previously the goroutine
  kept running and results were silently discarded.
- ResumeBackend launches a fresh probe goroutine on the existing worker,
  preserving transition history. The backend re-enters unknown state.

Integration tests (tests/01-maglevd/)
- Containerlab topology with 3 nginx:alpine backends on a dedicated
  management network (172.20.30.0/24) with static IPs.
- maglevd config with 200ms HTTP health-check interval for fast test
  convergence (rise=2, fall=2).
- 8 test cases: deploy lab, start maglevd, all backends reach up,
  nginx logs confirm probes arriving, pause stops probes (probe count
  stable), resume restarts probes, disable stops probes, enable
  restarts probes.

VPP dataplane test (tests/02-vpp-lb/)
- Rewrite 01-e2e-lab.robot to match the actual single-VPP topology:
  test client-to-server ping through VPP bridge domains and verify
  nginx is serving on all app servers. The previous version referenced
  a non-existent topology file and tested OSPF/BFD between two VPP
  nodes that don't exist in this lab.

Build infrastructure
- Add 'make robot-test' target with TEST= for suite selection.
- Add tests/.venv target for Robot Framework virtualenv.
- Make IMAGE optional in rf-run.sh.
- Add .gitignore entries for test output, venv, logs, and clab state.

tests/01-maglevd/01-healthcheck.robot

@@ -0,0 +1,135 @@
+*** Settings ***
+Library             OperatingSystem
+Library             Process
+Resource            ../common.robot
+
+Suite Setup         Setup Suite
+Suite Teardown      Cleanup Suite
+
+
+*** Variables ***
+${lab-name}         maglevd-test
+${lab-file}         maglevd-lab/maglevd.clab.yml
+${config-file}      maglevd-lab/maglev.yaml
+${runtime}          docker
+${GRPC_PORT}        9091
+
+
+*** Test Cases ***
+Deploy maglevd-test lab
+    ${rc}    ${output} =    Run And Return Rc And Output
+    ...    ${CLAB_BIN} --runtime ${runtime} deploy -t ${CURDIR}/${lab-file}
+    Log    ${output}
+    Should Be Equal As Integers    ${rc}    0
+
+Start maglevd
+    ${handle} =    Start Process    ${MAGLEVD}
+    ...    --config    ${CURDIR}/${config-file}
+    ...    --grpc-addr    :${GRPC_PORT}
+    ...    --log-level    debug
+    ...    alias=maglevd    stdout=${EXECDIR}/tests/out/maglevd.log
+    ...    stderr=STDOUT
+    Set Suite Variable    ${MAGLEVD_HANDLE}    ${handle}
+    Sleep    3s    Wait for nginx containers and probes to converge
+
+All backends reach up state
+    [Template]    Backend Should Be Up
+    nginx1
+    nginx2
+    nginx3
+
+Health checks are reaching all backends
+    [Template]    Probe Count Should Be Positive
+    nginx1
+    nginx2
+    nginx3
+
+Pause backend stops probing
+    Maglevc    set backend nginx1 pause
+    Backend Should Have State    nginx1    paused
+    Sleep    1s
+    ${before} =    Get Probe Count    nginx1
+    Sleep    2s    Wait to confirm no new probes arrive
+    ${after} =    Get Probe Count    nginx1
+    Should Be True    ${after} == ${before}
+    ...    Probe count for nginx1 grew while paused: ${before} → ${after}
+
+Resume backend restarts probing
+    Maglevc    set backend nginx1 resume
+    ${before} =    Get Probe Count    nginx1
+    Sleep    2s    Wait for resumed probes to accumulate
+    ${after} =    Get Probe Count    nginx1
+    Should Be True    ${after} > ${before}
+    ...    Probe count for nginx1 did not grow after resume: ${before} → ${after}
+    Wait Until Keyword Succeeds    5s    500ms
+    ...    Backend Should Be Up    nginx1
+
+Disable backend stops probing
+    Maglevc    set backend nginx2 disable
+    Backend Should Have State    nginx2    removed
+    Backend Should Be Disabled    nginx2
+    Sleep    1s
+    ${before} =    Get Probe Count    nginx2
+    Sleep    2s    Wait to confirm probes stopped
+    ${after} =    Get Probe Count    nginx2
+    Should Be True    ${after} == ${before}
+    ...    Probe count for nginx2 grew while disabled: ${before} → ${after}
+
+Enable backend restarts probing
+    Maglevc    set backend nginx2 enable
+    ${before} =    Get Probe Count    nginx2
+    Sleep    2s    Wait for re-enabled probes to accumulate
+    ${after} =    Get Probe Count    nginx2
+    Should Be True    ${after} > ${before}
+    ...    Probe count for nginx2 did not grow after enable: ${before} → ${after}
+    Wait Until Keyword Succeeds    5s    500ms
+    ...    Backend Should Be Up    nginx2
+
+
+*** Keywords ***
+Setup Suite
+    ${arch} =    Run    go env GOARCH
+    Set Suite Variable    ${ARCH}    ${arch}
+    Set Suite Variable    ${MAGLEVD}    ${EXECDIR}/build/${ARCH}/maglevd
+    Set Suite Variable    ${MAGLEVC}    ${EXECDIR}/build/${ARCH}/maglevc
+
+Cleanup Suite
+    Run Keyword And Ignore Error    Terminate Process    maglevd    kill=true
+    Run    ${CLAB_BIN} --runtime ${runtime} destroy -t ${CURDIR}/${lab-file} --cleanup
+
+Maglevc
+    [Documentation]    Run a maglevc command and return its output.
+    [Arguments]    ${cmd}
+    ${rc}    ${output} =    Run And Return Rc And Output
+    ...    ${MAGLEVC} --server\=localhost:${GRPC_PORT} --color\=false ${cmd}
+    Log    ${output}
+    Should Be Equal As Integers    ${rc}    0
+    RETURN    ${output}
+
+Backend Should Be Up
+    [Arguments]    ${name}
+    ${output} =    Maglevc    show backends ${name}
+    Should Match Regexp    ${output}    state\\s+up
+
+Backend Should Have State
+    [Arguments]    ${name}    ${expected_state}
+    ${output} =    Maglevc    show backends ${name}
+    Should Match Regexp    ${output}    state\\s+${expected_state}
+
+Backend Should Be Disabled
+    [Arguments]    ${name}
+    ${output} =    Maglevc    show backends ${name}
+    Should Match Regexp    ${output}    enabled\\s+false
+
+Get Probe Count
+    [Documentation]    Return the number of HTTP health-check requests seen in a backend's nginx log.
+    [Arguments]    ${name}
+    ${output} =    Run    docker logs clab-${lab-name}-${name} 2>/dev/null | grep -c "GET /" || echo 0
+    ${count} =    Convert To Integer    ${output.strip()}
+    RETURN    ${count}
+
+Probe Count Should Be Positive
+    [Arguments]    ${name}
+    ${count} =    Get Probe Count    ${name}
+    Should Be True    ${count} > 0
+    ...    No health-check requests found in nginx logs for ${name}

tests/01-maglevd/maglevd-lab/maglev.yaml

@@ -0,0 +1,43 @@
+maglev:
+  healthchecker:
+    transition-history: 5
+
+  healthchecks:
+    http-check:
+      type: http
+      port: 80
+      params:
+        path: /
+        response-code: "200"
+      interval: 200ms
+      fast-interval: 100ms
+      down-interval: 1s
+      timeout: 1s
+      rise: 2
+      fall: 2
+
+  backends:
+    nginx1:
+      address: 172.20.30.11
+      healthcheck: http-check
+    nginx2:
+      address: 172.20.30.12
+      healthcheck: http-check
+    nginx3:
+      address: 172.20.30.13
+      healthcheck: http-check
+
+  frontends:
+    http-vip:
+      description: "Test HTTP VIP"
+      address: 192.0.2.1
+      protocol: tcp
+      port: 80
+      pools:
+        - name: primary
+          backends:
+            nginx1: {}
+            nginx2: {}
+        - name: fallback
+          backends:
+            nginx3: {}

tests/01-maglevd/maglevd-lab/maglevd.clab.yml

@@ -0,0 +1,20 @@
+name: maglevd-test
+
+mgmt:
+  network: maglevd-test-net
+  ipv4-subnet: 172.20.30.0/24
+
+topology:
+  nodes:
+    nginx1:
+      kind: linux
+      image: nginx:alpine
+      mgmt-ipv4: 172.20.30.11
+    nginx2:
+      kind: linux
+      image: nginx:alpine
+      mgmt-ipv4: 172.20.30.12
+    nginx3:
+      kind: linux
+      image: nginx:alpine
+      mgmt-ipv4: 172.20.30.13