Pools, CLI, versioning, Debian packaging, HTTPS fix

- Replaced flat `backends: [...]` list on frontends with an ordered `pools:`
  list; each pool has a name and a map of backends with per-pool weights (0–100,
  default 100). Pools express priority: first pool with a healthy backend wins.
- Removed global backend weight (was on the backend, now lives in the pool).
- Config validation enforces non-empty pools, non-empty pool names, weight
  range, and consistent address families across all pools of a frontend.

- Added `PoolBackendInfo { name, weight }` and changed `PoolInfo.backends` from
  `repeated string` to `repeated PoolBackendInfo` so weights are visible over
  the API.

- Full interactive shell with readline, tab completion, and `?` inline help.
- Command tree parser (Walk) handles fixed keywords and dynamic slot nodes;
  prefix matching with exact-match priority.
- Commands: `show version/frontends/frontend/backends/backend/healthchecks/
  healthcheck`, `set backend <name> pause|resume`, `quit`/`exit`.
- `show frontend` output is hierarchical (pools → backends) with per-backend
  weights and `[disabled]` notation; pool section uses fixed-width formatting
  so ANSI color codes don't corrupt tabwriter alignment.
- `-color` flag (default true) wraps static field labels in dark-blue ANSI;
  works correctly with tabwriter because all labels carry identical-length
  escape sequences.

- `cmd/version.go` package holds `version`, `commit`, `date` vars set at build
  time via `-ldflags -X`.
- `make build` / `make build-amd64` / `make build-arm64` all inject
  `VERSION=0.1.1`, `COMMIT_HASH` (from `git rev-parse --short HEAD`), and
  `DATE` (UTC ISO-8601).
- `maglevc` prints version on interactive startup and exposes `show version`.
- `maglevd` logs version/commit/date at startup; `-version` flag prints and exits.

- `doHTTPProbe` was building a `https://` target URL even though TLS was already
  applied to the connection inside `inNetns`. `http.Transport` then wrapped the
  connection in a second TLS layer, producing "http: server gave HTTP response
  to HTTPS client". Fixed by always using `http://` in the target URL.
- Added `TestHTTPSProbe` using `httptest.NewTLSServer` to cover the full path.

- New `docs/user-guide.md`: maglevd flags/signals, maglevc commands, shell
  completion, and command-tree parser walkthrough.
- New `docs/healthchecks.md`: state machine, rise/fall model, probe intervals,
  all transition events with log examples.
- Updated `docs/config-guide.md`: pools design, removed global weight from
  backends, updated all examples.
- Updated `README.md`: packaging table, build paths, corrected binary locations
  (`/usr/sbin/maglevd`), config filename (`.yaml`).

- `debian/` directory contains `control.in`, `maglevd.service`, `default.maglev`,
  `maglev.yaml` (example config), `conffiles`, `postinst`, `prerm`.
- `debian/build-deb.sh` stages a package tree and calls `dpkg-deb`; emits
  `build/vpp-maglev_<version>~<commit>_<arch>.deb`.
- Cross-compiles for amd64 and arm64 in one `make pkg-deb` invocation.
- `maglevd` installed to `/usr/sbin/`, `maglevc` to `/usr/bin/`.
- Service reads `MAGLEV_CONFIG` from `/etc/default/maglev`
  (default: `/etc/maglev/maglev.yaml`).
- Man pages `maglevd(8)` and `maglevc(1)` live in `docs/` and are gzip'd into
  the package.
- All build output goes to `build/<arch>/`; `build/` is gitignored.

internal/checker/checker.go

@@ -208,9 +208,16 @@ func (c *Checker) ListFrontendBackends(frontendName string) []*health.Backend {
 		return nil
 	}
 	var out []*health.Backend
-	for _, name := range fe.Backends {
-		if w, ok := c.workers[name]; ok {
-			out = append(out, w.backend)
+	seen := map[string]struct{}{}
+	for _, pool := range fe.Pools {
+		for name := range pool.Backends {
+			if _, already := seen[name]; already {
+				continue
+			}
+			seen[name] = struct{}{}
+			if w, ok := c.workers[name]; ok {
+				out = append(out, w.backend)
+			}
 		}
 	}
 	return out
@@ -398,15 +405,22 @@ func (c *Checker) runProbe(ctx context.Context, name string, pos, total int) {
 	}
 }
 
-// emitForBackend emits one Event per frontend that references backendName,
-// using the provided frontends map. Must be called with c.mu held.
+// emitForBackend emits one Event per frontend that references backendName
+// (in any pool), using the provided frontends map. Must be called with c.mu held.
 func (c *Checker) emitForBackend(backendName string, addr net.IP, t health.Transition, frontends map[string]config.Frontend) {
 	for feName, fe := range frontends {
-		for _, name := range fe.Backends {
-			if name == backendName {
-				c.emit(Event{FrontendName: feName, BackendName: backendName, Backend: addr, Transition: t})
+		emitted := false
+		for _, pool := range fe.Pools {
+			if emitted {
 				break
 			}
+			for name := range pool.Backends {
+				if name == backendName {
+					c.emit(Event{FrontendName: feName, BackendName: backendName, Backend: addr, Transition: t})
+					emitted = true
+					break
+				}
+			}
 		}
 	}
 }
@@ -491,13 +505,15 @@ func tcpParamsEqual(a, b *config.TCPParams) bool {
 }
 
 // activeBackendNames returns a sorted, deduplicated list of backend names that
-// are referenced by at least one frontend and have Enabled: true.
+// are referenced by at least one frontend pool and have Enabled: true.
 func activeBackendNames(cfg *config.Config) []string {
 	seen := map[string]struct{}{}
 	for _, fe := range cfg.Frontends {
-		for _, name := range fe.Backends {
-			if b, ok := cfg.Backends[name]; ok && b.Enabled {
-				seen[name] = struct{}{}
+		for _, pool := range fe.Pools {
+			for name := range pool.Backends {
+				if b, ok := cfg.Backends[name]; ok && b.Enabled {
+					seen[name] = struct{}{}
+				}
 			}
 		}
 	}

internal/checker/checker_test.go

@@ -29,7 +29,6 @@ func makeTestConfig(interval time.Duration, fall, rise int) *config.Config {
 				Address:     net.ParseIP("10.0.0.2"),
 				HealthCheck: "icmp",
 				Enabled:     true,
-				Weight:      100,
 			},
 		},
 		Frontends: map[string]config.Frontend{
@@ -37,7 +36,11 @@ func makeTestConfig(interval time.Duration, fall, rise int) *config.Config {
 				Address:  net.ParseIP("192.0.2.1"),
 				Protocol: "tcp",
 				Port:     80,
-				Backends: []string{"be0"},
+				Pools: []config.Pool{
+					{Name: "primary", Backends: map[string]config.PoolBackend{
+						"be0": {Weight: 100},
+					}},
+				},
 			},
 		},
 	}
@@ -116,13 +119,16 @@ func TestReloadAddsBackend(t *testing.T) {
 		Address:     net.ParseIP("10.0.0.3"),
 		HealthCheck: "icmp",
 		Enabled:     true,
-		Weight:      100,
 	}
 	newCfg.Frontends["web2"] = config.Frontend{
 		Address:  net.ParseIP("192.0.2.2"),
 		Protocol: "tcp",
 		Port:     443,
-		Backends: []string{"be1"},
+		Pools: []config.Pool{
+			{Name: "primary", Backends: map[string]config.PoolBackend{
+				"be1": {Weight: 100},
+			}},
+		},
 	}
 
 	ctx, cancel := context.WithCancel(context.Background())
@@ -186,7 +192,11 @@ func TestSharedBackendProbedOnce(t *testing.T) {
 		Address:  net.ParseIP("192.0.2.3"),
 		Protocol: "tcp",
 		Port:     443,
-		Backends: []string{"be0"},
+		Pools: []config.Pool{
+			{Name: "primary", Backends: map[string]config.PoolBackend{
+				"be0": {Weight: 100},
+			}},
+		},
 	}
 
 	c := New(cfg)