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>

docs/future/AI_AGENTS_IDEAS.md

@@ -4,6 +4,15 @@ Backlog für das AI-Workbench / Mission-Runner-System (`services/mana-ai`, `@man
 
 Kontext: [`services/mana-ai/CLAUDE.md`](../../services/mana-ai/CLAUDE.md), [`docs/architecture/COMPANION_BRAIN_ARCHITECTURE.md`](../architecture/COMPANION_BRAIN_ARCHITECTURE.md).
 
+Was davon schon gelandet ist:
+- **Punkt 1 (Encrypted-Tables serverseitig)** → Mission-Key-Grant ausgerollt. Plan-Doc: [`../plans/ai-mission-key-grant.md`](../plans/ai-mission-key-grant.md).
+- **Named Agents + per-Agent-Policy + Budget + Observability** (war nicht auf dieser Liste, kam aus den Design-Gesprächen) → Multi-Agent Workbench ausgerollt. Plan-Doc: [`../plans/multi-agent-workbench.md`](../plans/multi-agent-workbench.md).
+
+Was aus dieser Liste noch offen ist: Punkte 2, 3, 4, 5, 6, 7, 8 unten — alle weiterhin relevant.
+
+Forward-looking Plans:
+- **Team-Workbench** (Multi-User + geteilter AI-Kontext): [`../plans/team-workbench.md`](../plans/team-workbench.md).
+
 Sortiert grob nach Impact.
 
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