refactor(fleet): rename tmux socket mosaic-factory → mosaic-fleet

Pure rename of the named production-isolation socket to match the product brand
(Mosaic Fleet), per Jason. Behavior is identical — only the socket NAME changes.

- 6 example presets: socket_name: mosaic-factory → mosaic-fleet
- fleet.ts: DEFAULT_SOCKET_NAME = 'mosaic-fleet' (+ all literals)
- systemd units + READMEs, roster.schema.json, start-agent-session.sh
- docs/guides + fleet PRD/TASKS + scratchpads; tests updated

The PoC roster is socket-LESS (default socket, no -L), so it is unaffected.
docs/fleet/north-star.md is intentionally EXCLUDED (owned by the in-flight
doctrine PR #629 — its mosaic-factory references are renamed there to avoid a
merge conflict). The live legacy canary fleet still running on the old socket is
a separate retire/migrate op, not this PR.

Single find/replace — target trivially swappable if the brand is reconsidered.

Verified: 172 fleet + onboarding tests green; tsc/eslint/prettier/sanitize clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EsgTQzV5YUGk1JtCLP4B83

docs/scratchpads/2026-06-20-fleet-cli-local-canary.md

@@ -17,7 +17,7 @@ Implement enough product surface to use the fleet locally:
 - roster schema and examples
 - local canary docs and rollback instructions
 - tests for CLI behavior where practical
-- canary verification on named tmux socket `mosaic-factory`
+- canary verification on named tmux socket `mosaic-fleet`
 
 ## Non-goals
 
@@ -30,7 +30,7 @@ Implement enough product surface to use the fleet locally:
 
 - CLI can initialize a minimal roster outside product defaults.
 - CLI can install user systemd units and fleet helper scripts to a configurable Mosaic home.
-- CLI can start/stop/status/verify a canary fleet using `mosaic-factory`.
+- CLI can start/stop/status/verify a canary fleet using `mosaic-fleet`.
 - `mosaic agent send` uses existing named-socket/exact-target tmux tooling.
 - `mosaic agent reset` targets only the named agent session on the named socket.
 - Verification proves default tmux sessions remain untouched.