PRE-RELEASE 0.9.2: frontend rename source→collector, tab layout fit

Rename the collector-picker concept to 'collector' throughout the
frontend so it no longer collides with the ipng_source_tag group-by
(which is labelled 'source'). Affects PageData.Collector, the raw
JSON output key, template labels, and tests. Proto Source field is
untouched (wire-level name used by CLI and aggregator too).

Shrink tab padding/gap/font-size and add window:/filter: labels so
the four tab rows (window, filter, collector, tor) line up and 7+
collectors fit on one line at the 1100px body width.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Makefile

@@ -5,7 +5,7 @@ PROTO_FILE   := $(PROTO_DIR)/logtail.proto
 GEN_FILES    := proto/logtailpb/logtail.pb.go proto/logtailpb/logtail_grpc.pb.go
 
 NATIVE_ARCH  := $(shell go env GOARCH)
-VERSION      := 0.9.1
+VERSION      := 0.9.2
 COMMIT_HASH  := $(shell git rev-parse --short HEAD 2>/dev/null || echo unknown)
 DATE         := $(shell date -u +%Y-%m-%dT%H:%M:%SZ)
 LDFLAGS      := -s -w \