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/pages/__tests__/Workspace.test.tsx

@@ -94,6 +94,12 @@ vi.mock("../../lib/api", async (importOriginal) => {
           recordCall("GET", `/api/lanes/${id}/git`);
           return { available: false };
         }),
+        // Same for the lane's own application stack: nothing here asserts on it,
+        // so report the "no .ccam/profile" shape, which is the common case.
+        runtime: vi.fn().mockImplementation(async (id: number) => {
+          recordCall("GET", `/api/lanes/${id}/runtime`);
+          return { available: false };
+        }),
         stage: vi.fn().mockImplementation(async () => {
           recordCall("POST", `/api/lanes/stage`);
           return { ok: true };