feat(ai): close the loop — server write-back + webapp staging effect

Completes the off-tab AI pipeline. mana-ai now writes produced plans
back to `sync_changes` as a server-sourced Mission iteration; the webapp
picks it up on next sync and translates each PlanStep into a local
Proposal via the existing createProposal flow. User sees the resulting
ghost cards in the matching module's AiProposalInbox with full mission
attribution.

Server (mana-ai v0.3):
- `db/connection.ts` — `withUser(sql, userId, fn)` RLS-scoped tx helper
  mirroring the Go `withUser` pattern (SET LOCAL app.current_user_id)
- `db/iteration-writer.ts`
  - `planToIteration(plan, id, now)` — shared-ai AiPlanOutput → inline
    MissionIteration with `source: 'server'` + status='awaiting-review'
  - `appendServerIteration(sql, input)` — INSERT sync_changes row with
    op=update, data={iterations: [...]} + field_timestamps + actor
    JSONB={kind:'system', source:'mission-runner'}
- `cron/tick.ts` — after parse success: build iteration, append to
  mission.iterations, persist via appendServerIteration. Stats now
  include `plansWrittenBack`.

Actor union:
- `packages/shared-ai/src/actor.ts` + webapp actor: `system.source` gains
  `'mission-runner'` so the server's own writes are attributed correctly
  and distinguishable from projection/rule writes

Webapp:
- `data/ai/missions/server-iteration-staging.ts`
  - `startServerIterationStaging()` subscribes to aiMissions via Dexie
    liveQuery; on each Mission update, walks iterations looking for
    `source='server'` entries that haven't been staged yet
  - For each such iteration: creates a Proposal per PlanStep under
    `{kind:'ai', missionId, iterationId, rationale}` so policy + hooks
    fire correctly
  - Writes proposalIds back into plan[].proposalId + status='staged' so
    other tabs and app restarts skip re-staging
  - Idempotent: in-memory `processedIterations` Set + durable
    proposalId marker
- Wired into (app)/+layout.svelte alongside startMissionTick
- 3 unit tests: translate server iteration → proposal, skip
  already-staged, ignore browser iterations

Full pipeline now: user creates Mission in /companion/missions →
mana-ai tick picks it up → calls mana-llm → parses plan →
writes iteration → synced to webapp → staging effect creates
proposals → user approves in /todo (or any module) → task lands with
`{actor: ai, missionId, iterationId, rationale}` attribution.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/shared-ai/src/actor.ts

@@ -18,7 +18,7 @@ export type Actor =
 	  }
 	| {
 			readonly kind: 'system';
-			readonly source: 'projection' | 'rule' | 'migration';
+			readonly source: 'projection' | 'rule' | 'migration' | 'mission-runner';
 	  };
 
 export const USER_ACTOR: Actor = Object.freeze({ kind: 'user' });