docs: flesh out Multi-Agent plan shipping log + Team Workbench forward plan

The Multi-Agent Workbench shipped end-to-end (commits 1771063df through
7c89eb625). This commit turns the plan doc into a proper history + post-
mortem and captures the deferred Team-Workbench as its own forward plan
so the architectural breadcrumbs don't rot.

docs/plans/multi-agent-workbench.md:
- Status bumped to ✅ Shipped; every phase checkbox flipped.
- Open-questions section rewritten with the decisions that were
  actually made (name-unique via store write-time check, per-source
  system principalIds, policy fully migrated, scene binding default-
  empty with smart suggestion).
- New "Shipping-Historie" table mapping each phase to its commit, the
  number of files touched, and the test outcome.
- New "Lessons Learnt + Follow-Up Ideen" with:
  * What went better than expected (L3 Actor cutover, getOrCreate
    instead of unique index, displayName caching)
  * Thin spots worth revisiting (avatar not on Actor, missing token
    counter for budget, no missions list on agent detail, no
    drag-reassign, scene binding doesn't drive filters yet)
  * Five deferred follow-up projects (team features, agent memory
    self-update, agent-to-agent messaging, meta-planner, per-agent
    encryption domains)

docs/plans/team-workbench.md (NEW):
- Full forward-looking plan for the deferred Team-Workbench.
- Two use-cases (human multi-user vs multi-agent sharing team
  context) with the observation that they share the same infra.
- Decision candidates table (still open — meant as T0 RFC fodder,
  not baked in).
- Architecture sketch with data-model deltas over the current
  single-user shape.
- Encryption subsection dedicated to the hardest problems: team-key
  wrapping per member (reuses Mission-Grant pattern), member-removal
  rotation (lazy vs eager), Zero-Knowledge-mode incompatibility.
- T0..T6 phasing (~7 weeks for a clean first-pass).
- Section "Wie Multi-Agent dafür den Weg geebnet hat" enumerating
  the four invariants the shipped Phase 0-7 deliberately preserved
  to make this plan cheap when it lands.

docs/plans/README.md (NEW):
- Index doc with the AI/Workbench roadmap as an ASCII flow so future
  contributors can locate themselves in the sequence without reading
  three 400-line plans first.

docs/future/AI_AGENTS_IDEAS.md:
- Header marks Point 1 (encrypted tables) as shipped via the Mission
  Grant plan; points 2-8 stay relevant. Cross-link to all three plan
  docs so this stays the go-to backlog.

services/mana-ai/CLAUDE.md:
- Design-context header expanded to link to all four related docs
  (arch §20-22, both shipped plans, forward team plan, ideas backlog).

No code changes.

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

services/mana-ai/CLAUDE.md

@@ -2,7 +2,12 @@
 
 Background runner for the AI Workbench. Picks up due Missions from the `mana_sync` Postgres and plans/proposes next steps without requiring an open browser tab. Complements the foreground `startMissionTick` in the webapp (`apps/mana/apps/web/src/lib/data/ai/missions/setup.ts`).
 
-Design context: [`docs/architecture/COMPANION_BRAIN_ARCHITECTURE.md` §20](../../docs/architecture/COMPANION_BRAIN_ARCHITECTURE.md).
+Design context:
+- [`docs/architecture/COMPANION_BRAIN_ARCHITECTURE.md`](../../docs/architecture/COMPANION_BRAIN_ARCHITECTURE.md) §20 (AI Workbench base), §21 (Mission Key-Grants), §22 (Multi-Agent Workbench)
+- [`docs/plans/ai-mission-key-grant.md`](../../docs/plans/ai-mission-key-grant.md) — Shipped (per-mission key-grant for encrypted inputs)
+- [`docs/plans/multi-agent-workbench.md`](../../docs/plans/multi-agent-workbench.md) — Shipped (named agents, per-agent policy/memory, scene lens)
+- [`docs/plans/team-workbench.md`](../../docs/plans/team-workbench.md) — Forward-looking (multi-user + shared team context)
+- [`docs/future/AI_AGENTS_IDEAS.md`](../../docs/future/AI_AGENTS_IDEAS.md) — Unshipped improvement backlog
 
 ## Status: v0.3 (full close-the-loop)