docs(architecture): fix YAML-invalid frontmatter; changelog text moves to notes

- last_updated annotations containing ': ' ('family composition: ...',
  'feature graph re-pinned: ...', 'REQ-5 added: ...') broke Gitea's
  frontmatter parser in docs/architecture/README.md,
  backends-and-dispatch.md, and requirements.md
- last_updated is now a bare date; the annotation lives in a quoted
  notes field across all annotated architecture docs
- convention documented in .opencode/agents/architect.md: bare
  last_updated date, quoted notes, quotes required for ': ' scalars

Verification: all docs/**/*.md frontmatter parsed with yaml.safe_load
(16/16 OK); cargo test, clippy --all-targets -D warnings, fmt --check pass

.opencode/agents/architect.md

@@ -116,9 +116,14 @@ All architecture documents use YAML frontmatter:
 ---
 status: draft | reviewed | stable | deprecated
 last_updated: YYYY-MM-DD
+notes: "optional one-line change summary"
 ---
 ```
 
+`last_updated` must be a bare date and any annotation text lives in `notes`.
+Both `notes` and multi-word values must be double-quoted — Gitea's frontmatter
+parser rejects unquoted scalars containing `: `.
+
 | Status | Meaning | Transitions |
 |--------|---------|-------------|
 | `draft` | Under active development. May change significantly. | → `reviewed` when open questions are resolved |

docs/architecture/README.md

@@ -1,6 +1,7 @@
 ---
 status: draft
-last_updated: 2026-10-11 (ADR-013 — family composition: no sibling dependency in-core, sweep-lease semantics, co-tenancy/no-cross-store-atomicity rulings, OQ-11 resolved, feature graph re-pinned to engine features)
+last_updated: 2026-10-11
+notes: "ADR-013 — family composition: no sibling dependency in-core, sweep-lease semantics, co-tenancy/no-cross-store-atomicity rulings, OQ-11 resolved, feature graph re-pinned to engine features"
 ---
 
 # alkblobs — Architecture

docs/architecture/backends-and-dispatch.md

@@ -1,6 +1,7 @@
 ---
 status: draft
-last_updated: 2026-10-11 (ADR-013 — feature graph re-pinned: engine features pull their own drivers; `kv`/`large` tier features retired, `sqlite` default-on, `local` ungated)
+last_updated: 2026-10-11
+notes: "ADR-013 — feature graph re-pinned: engine features pull their own drivers; kv/large tier features retired, sqlite default-on, local ungated"
 ---
 
 # Backends, tiers, and dispatch

docs/architecture/gc-and-namespaces.md

@@ -1,6 +1,7 @@
 ---
 status: draft
-last_updated: 2026-10-11 (ADR-013 — sweeper-lock semantics pinned as the named exclusive sweep lease; provider unchanged; composition boundary referenced)
+last_updated: 2026-10-11
+notes: "ADR-013 — sweeper-lock semantics pinned as the named exclusive sweep lease; provider unchanged; composition boundary referenced"
 ---
 
 # Pooling, namespaces, and GC

docs/architecture/open-questions.md

@@ -1,6 +1,7 @@
 ---
 status: draft
-last_updated: 2026-10-11 (ADR-013 round — OQ-11 resolved on in-tree evidence; the parked index is now empty)
+last_updated: 2026-10-11
+notes: "ADR-013 round — OQ-11 resolved on in-tree evidence; the parked index is now empty"
 ---
 
 # Open Questions

docs/architecture/ops-surface.md

@@ -1,6 +1,7 @@
 ---
 status: draft
-last_updated: 2026-10-03 (ADR-012 §2 — put response {token, digest}; have token-renewal form; fetch verification wording; non-fleet token scope)
+last_updated: 2026-10-03
+notes: "ADR-012 §2 — put response {token, digest}; have token-renewal form; fetch verification wording; non-fleet token scope"
 ---
 
 # Ops surface (alkcall-backed network operations)

docs/architecture/overview.md

@@ -1,6 +1,7 @@
 ---
 status: draft
-last_updated: 2026-10-11 (ADR-013 — family composition & reactive boundary; OQ-11 resolved, feature graph re-pinned to engine features)
+last_updated: 2026-10-11
+notes: "ADR-013 — family composition & reactive boundary; OQ-11 resolved, feature graph re-pinned to engine features"
 ---
 
 # Overview

docs/architecture/requirements.md

@@ -1,6 +1,7 @@
 ---
 status: draft
-last_updated: 2026-10-11 (ADR-013 composition round — REQ-5 added: the family's first consumers deploy this crate with the sibling reactive substrate; co-tenancy + liveness-form facts pinned)
+last_updated: 2026-10-11
+notes: "ADR-013 composition round — REQ-5 added: the family's first consumers deploy this crate with the sibling reactive substrate; co-tenancy + liveness-form facts pinned"
 ---
 
 # Requirements

docs/architecture/store-api.md

@@ -1,6 +1,7 @@
 ---
 status: draft
-last_updated: 2026-10-11 (ADR-013 — the fleet sweeper lock's semantics pinned as the named exclusive sweep lease; provider unchanged; composition boundary referenced)
+last_updated: 2026-10-11
+notes: "ADR-013 — the fleet sweeper lock's semantics pinned as the named exclusive sweep lease; provider unchanged; composition boundary referenced"
 ---
 
 # Store API