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/fleet/PRD.md

@@ -7,10 +7,10 @@
 
 ## Problem
 
-The durable tmux fleet runs on the isolated `mosaic-factory` socket. That isolation
+The durable tmux fleet runs on the isolated `mosaic-fleet` socket. That isolation
 (which protects the operator's default tmux) makes the fleet **invisible** to default
 tooling, and truth is split across three planes no single command joins — systemd
-(`systemctl --user`), tmux (`-L mosaic-factory`), and the process tree (`pstree`).
+(`systemctl --user`), tmux (`-L mosaic-fleet`), and the process tree (`pstree`).
 `agent tail` (`capture-pane`) returns **blank for full-screen TUIs**, and `agent send`
 confirms only keystroke injection, not acceptance. Net: the operator has near-zero
 observability and no safe way to watch a session.
@@ -56,7 +56,7 @@ observability and no safe way to watch a session.
 
 ## Acceptance criteria
 
-- `mosaic fleet ps` shows all 5 live sessions on `mosaic-factory` with correct
+- `mosaic fleet ps` shows all 5 live sessions on `mosaic-fleet` with correct
   pane/pid/idle and flags the dogfood **drift** (`canary-pi` runtime=pi but pane runs
   `dogfood-agent.py`) and the **boot-enable** gap (active but disabled).
 - Killing one agent's pane flips its row to dead/stale within one `interval`.
@@ -72,7 +72,7 @@ observability and no safe way to watch a session.
 - Unit/CLI specs in `packages/mosaic/src/commands/fleet.spec.ts` (and a new
   `fleet-ps`/`watch`/`send-verify` spec) using the injected `CommandRunner` to assert
   exact tmux/systemd command construction and JSON shape (tenant+host present).
-- Situational: run against the live `mosaic-factory` fleet; capture `fleet ps` output,
+- Situational: run against the live `mosaic-fleet` fleet; capture `fleet ps` output,
   a kill-and-detect cycle, a read-only `watch`, and a `send --verify` pass/fail pair.
 
 ## Known limitations