feat: token usage tracking with JSONL tailer and Supabase storage

[DarlingtonDeveloper]

Summary

• Adds JSONL file tailer that reads anthropic-payload.jsonl, accumulates per-session token/cost data, and flushes to Postgres (Supabase) every 30s
• CC sidecar swarm.cc.session.completed events enrich rows with duration, exit code, and files changed via EnrichSession upsert
• Usage API on admin mux (:9090) exposes /api/usage/summary, /api/usage/agent/{id}, /api/usage/model/{id}, and /api/usage/cost-efficiency/{id} for Dispatch routing
• Both tailer and sidecar use INSERT ON CONFLICT upserts that don't overwrite each other's fields — order-independent row convergence

New packages

Package	Purpose
internal/store	UsageStore interface, PostgresStore (pgxpool), EnsureSchema migration
internal/tailer	JSONL tailer with offset persistence, in-memory accumulators, periodic flush
internal/usage	HTTP API handlers mounted on admin mux behind existing auth

Modified files

• internal/config/config.go — DatabaseURL, UsageConfig (enabled, jsonl_path, flush/poll intervals), WARREN_DATABASE_URL env override
• internal/process/subscriber.go — usageStore field, enrichSession() called from completed/failed handlers
• cmd/orchestrator/main.go — wires store → schema → tailer → usage handlers → subscriber

Test plan

• go build ./... — clean
• go vet ./... — clean
• All existing tests pass (39 tests across admin, config, process, etc.)
• New unit tests: store types (4), tailer (8 including offset persistence, truncation detection, flush), usage handlers (9 including method validation, range parsing), config usage (3 including env override)
• Integration: run with Supabase, verify sessions appear via curl localhost:9090/api/usage/summary?range=30d
• Verify enrichment: trigger CC session completion, check completed_at/duration_ms/exit_code populated

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