feat(mosaic): mosaic update re-seeds framework + relaunches agents (#609)

Closes R13 (F3-m3). mosaic update installed the new npm CLI but never
re-seeded ~/.config/mosaic from the package's bundled framework/, so shipped
launcher/runtime changes (agent-name export + native HB) stayed DORMANT until
a manual re-seed — operators got the new CLI on a stale framework.

- update-checker.ts: resolveBundledFrameworkRoot, buildReseedCommand (install.sh
  in MOSAIC_SYNC_ONLY=1 MOSAIC_INSTALL_MODE=keep — the P4 data-safe reconcile:
  framework-owned overwrite + backup-once; SOUL/USER/*.local/credentials kept),
  runFrameworkReseed, readRosterAgentNames, buildRelaunchCommands.
- cli.ts update: after a successful CLI install that includes @mosaicstack/mosaic,
  re-seed the framework (default-on; --no-reseed to skip). Then --relaunch restarts
  rostered agents (systemctl --user restart mosaic-agent@<name>), else prints clear
  activation guidance. Only re-seeds when the framework-bearing package updated.

Flow: update CLI -> re-seed framework (data-safe) -> relaunch agents (opt-in).

Verified: 6 new unit tests + 19 runtime + 26 launch tests green; tsc/eslint/
prettier clean. Sync data-safety already proven (P4 matrix + live validation).

Refs #609

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

docs/TASKS.md

@@ -54,3 +54,7 @@ Active workstream is **W1 — Federation v1**. Workers should:
 ## P6 — Docs, compliance matrix, alpha tag (#606) — feat/p6-docs-compliance-alpha
 
 - Status: in-repo deliverables done (CONTRIBUTING.md + harness×gate compliance matrix + check-resident-budget.sh + CI wiring + ALPHA-DOD.md). Remaining: alpha tag v0.0.39-alpha (Lead, post-merge). aiguide reconcile merged (#8). Detail: scratchpads/p6-docs-compliance-alpha.md.
+
+## F3-m3 — mosaic update re-seeds framework + relaunches agents (#609) — feat/f3-m3-update-reseed
+
+- Status: implemented + tested. Closes R13: `mosaic update` now re-seeds the framework (data-safe MOSAIC_SYNC_ONLY) after the CLI install so shipped launcher/runtime changes activate; `--relaunch` restarts rostered agents; `--no-reseed` opts out. Detail: scratchpads/f3-m3-update-reseed.md.