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/plans/README.md

@@ -0,0 +1,51 @@
+# Plans
+
+Design + rollout plans, grouped by topic. Plans are long-form docs with
+baked-in decisions, phasing, open questions, and (when shipped) a
+history section with commit refs.
+
+## AI / Workbench roadmap
+
+The Mana AI Workbench has evolved in three successive planned waves —
+each one laying foundations the next one relies on:
+
+```
+  User hat einen Companion (v0 — shipped before these docs)
+        │
+        ▼
+  AI Missions + Proposals + Policy + Revert
+        │
+        ▼
+  Mission Key-Grants  ←  ai-mission-key-grant.md  ✅
+    (encrypted inputs decryptable by the server runner)
+        │
+        ▼
+  Multi-Agent Workbench  ←  multi-agent-workbench.md  ✅
+    (named agents, per-agent policy/memory/budget,
+     identity-aware Actor, scene→agent lens)
+        │
+        ▼
+  Team Workbench  ←  team-workbench.md  📝 (not started)
+    (multi-user + shared AI context,
+     admin lens on team members)
+```
+
+| Plan | Status | Scope |
+|---|---|---|
+| [`ai-mission-key-grant.md`](./ai-mission-key-grant.md) | ✅ Shipped | Per-mission RSA-wrapped key grant so `mana-ai` can decrypt allowlisted encrypted records when user opts in. |
+| [`multi-agent-workbench.md`](./multi-agent-workbench.md) | ✅ Shipped | Identity-aware Actor + named AI agents owning missions + per-agent policy + scene lens. |
+| [`team-workbench.md`](./team-workbench.md) | 📝 Forward-looking | TeamSpace with membership, team-encrypted records, admin lens on team members. Reuses Actor.principalId + key-wrapping patterns from the two above. |
+
+Cross-references:
+
+- Architecture narrative: [`docs/architecture/COMPANION_BRAIN_ARCHITECTURE.md`](../architecture/COMPANION_BRAIN_ARCHITECTURE.md) §20 (AI Workbench base), §21 (Mission Grants), §22 (Multi-Agent)
+- Non-plan ideas backlog: [`docs/future/AI_AGENTS_IDEAS.md`](../future/AI_AGENTS_IDEAS.md)
+- Service-internal notes: [`services/mana-ai/CLAUDE.md`](../../services/mana-ai/CLAUDE.md)
+- Webapp-internal notes: [`apps/mana/CLAUDE.md`](../../apps/mana/CLAUDE.md) → "AI Workbench" section
+
+## Other plans
+
+| Plan | Topic |
+|---|---|
+| [`mail-module-plan.md`](./mail-module-plan.md) | Mail module — IMAP/SMTP integration |
+| [`news-research-module.md`](./news-research-module.md) | News + research pipeline |