release prep: v0.1.3

[lsaether]

Cuts v0.1.3 — rooms + RFD #533 attach polish.

• Bump `Cargo.toml` from 0.1.2 → 0.1.3 (lock regenerated).
• Move all `## Unreleased` content into `## v0.1.3 — 2026-05-27` and backfill entries for shipped-but-not-yet-changelogged PRs (feat: add RFD 533-inspired attach/detach foundation #46, feat: add attach response replay ordering #47, feat: allow clients to skip legacy replay #50, feat: stream session attach history #53, fix: extend control-plane agent timeout #34, feat: publish session context cwd #35, fix: block unsafe agent client-tool fanout #36, feat: replay agent request openings #33).
• Add a fresh empty `## Unreleased` above for the next round.

Highlights since v0.1.2

• Rooms abstraction with compaction-aware transcripts (#58) and cross-segment turn-bookend carry in `historyPolicy: full` (#59). Closes #56. Spec: `docs/design/rooms.md`.
• RFD #533-inspired `session/attach` + `session/detach` foundation (#46) with replay ordering (#47), streamed history delivery (#53), and `?replay=skip` opt-out for attach-aware clients (#50).
• `amux/*` active-turn controls: hard-steer (#41), queue (#41), cancel (#30) — plus replay-safe agent request lifecycle openings (#33).
• Safe-by-default client-tool blocking (#36): `fs/` and `terminal/` are rejected with structured `-32000` to the agent; `--unsafe-debug-client-tool-broadcast` restores the old fanout for diagnostics.
• `amux/session_context` surfaces the mux/agent cwd (#35).

Breaking changes

• `?session=` → `?room=` (one-release deprecation alias).
• `amux/*` frame field `sessionId` → `roomId` where it referred to the mux id.
• `session/list` decoration field `proxySessionId` → `roomId`.
• `/debug/sessions` JSON keys renamed (`sessions`/`sessionCount` → `rooms`/`roomCount`; per-room `sessionId` → `roomId`).
• Library type renames (`SessionInner` → `RoomInner`, etc.; `src/session/` → `src/room/`).

Full list in `CHANGELOG.md`.

Validation

• `cargo fmt --check`
• `cargo clippy --all-targets -- -D warnings`
• `cargo test` — 63 unit + 78 integration = 141 tests

After this merges

I'll prepare an annotated tag `v0.1.3` against the merge commit and draft the GitHub release notes (mirroring the v0.1.2 release shape).