feat(cli): TUI slash command parsing + local commands (P8-009)

- Add parseSlashCommand() with regex-based parser for /cmd [args] format
- Add CommandRegistry with local-only commands (help, stop, cost, status, clear) and gateway manifest support
- Add short alias resolution: /n→new, /m→model, /t→thinking, /a→agent, /s→status, /h→help, /pref→preferences
- Add executeHelp() and executeStatus() local command handlers
- Extend Message.role union with 'system' for in-TUI system messages
- Handle commands:manifest socket event to update registry from gateway
- Wire InputBar to intercept /commands before sending to socket
- Render system messages as dimmed ⚙ prefix without avatar chrome
- Expose addSystemMessage() and socketRef from useSocket hook

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/TASKS.md

@@ -76,8 +76,8 @@
 | P7-021 | done        | Phase 7   | Verify Phase 7 — feature-complete platform E2E                                                     | —    | #132 W10 done |
 | P8-005 | done        | Phase 8   | CLI command architecture — DB schema + brain repo + gateway endpoints                              | #158 |               |
 | P8-006 | done        | Phase 8   | CLI command architecture — agent, mission, prdy commands + TUI mods                                | #158 |               |
-| P8-007 | not-started | Phase 8   | DB migrations — preferences.mutable + teams + team_members + projects.teamId                       | —    | #160          |
-| P8-008 | not-started | Phase 8   | @mosaic/types — CommandDef, CommandManifest, new socket events                                     | —    | #161          |
+| P8-007 | done        | Phase 8   | DB migrations — preferences.mutable + teams + team_members + projects.teamId                       | #175 | #160          |
+| P8-008 | done        | Phase 8   | @mosaic/types — CommandDef, CommandManifest, new socket events                                     | #174 | #161          |
 | P8-009 | not-started | Phase 8   | TUI Phase 1 — slash command parsing, local commands, system message rendering, InputBar wiring     | —    | #162          |
 | P8-010 | not-started | Phase 8   | Gateway Phase 2 — CommandRegistryService, CommandExecutorService, socket + REST commands           | —    | #163          |
 | P8-011 | not-started | Phase 8   | Gateway Phase 3 — PreferencesService, /preferences REST, /system Valkey override, prompt injection | —    | #164          |