feat(lanes): lane runtime UI, docs, and env additions (A1+A2)

Client-side rendering for the per-lane runtime facts (slot, ports,
database, Redis index, service liveness) added in the server-side
A1/A2 work, plus the doc updates (README, CLAUDE.md, docs/API.md,
client/server READMEs) describing the new profile.env keys, hook
environment contract, and REST endpoints.

client/src/components/lanes/__tests__/DestructiveLaneModal.test.tsx

@@ -47,6 +47,8 @@ function makeLane(overrides: Partial<Lane> = {}): Lane {
     liveness: "idle",
     detected_stage: null,
     detected_signal: null,
+    slot: null,
+    ports: {},
     ...overrides,
   };
 }