refactor(agent-runtime): replace dead litter-bridge gateway with metadata publisher

[0xSero]

Purpose

Delete the dead litter-bridge HTTP gateway (Design A) and keep only the litter-bridge.json metadata publishing that the KittyLitter daemon still reads.

The gateway served /api/litter-bridge/v1 on :8081 — a signed, versioned bridge forwarding controller-status, session-read, and agent-turn from the KittyLitter daemon. Design B replaced it with a scoped PiBridge on the daemon side (alleycat f443a83), and the alleycat HTTP client that called this endpoint was deleted in alleycat PR #34. The gateway was left running, used by nobody.

Key changes

The gateway did two things; only #2 is live:

1. Served /api/litter-bridge/v1 (dead — no caller remains).
2. Wrote litter-bridge.json publishing piAgentDir and piRuntime so the daemon launches the same Pi version and data dir this instance owns (live — alleycat reads it via load_gateway_metadata).

Extract #2 into a focused 150-line module (litter-bridge-metadata.ts) and delete the rest:

• services/agent-runtime/src/litter-bridge-gateway.ts (3,346 lines)
• services/agent-runtime/src/litter-bridge-mutation-ledger.ts (571 lines)
• services/agent-runtime/test/litter-bridge-gateway.test.ts (1,596 lines)
• services/agent-runtime/test/litter-bridge-mutation-ledger.test.ts (229 lines)
• shared/agent/litter-bridge.ts (700 lines) — only imported by the gateway
• shared/agent/litter-bridge.test.ts (526 lines)

server.ts drops the HTTP route and calls the new publisher's publishMetadata/dispose, which write and clean up the same litter-bridge.json with the same schema.

Size

• ~150 additions / 6,968 deletions across 8 files

Verification

• services/agent-runtime: bun test — 25 pass, 0 fail.
• services/agent-runtime: tsc --noEmit — clean.
• npm run check:contracts — passed.
• npm run check:structure — passed.

Notes

Depends conceptually on alleycat PR #34 (which deleted the HTTP client). The litter-bridge.json schema is unchanged, so the daemon's load_gateway_metadata continues to work. The install-desktop-app.sh change stashed on dev is unrelated and not included.