feat(929): delete db/yaml_legacy.rs entirely — CRDT is the sole source of truth

Final 929 sweep: every YAML-shaped helper is gone. No production code
parses or writes YAML front matter anywhere.

Surface removed:
- db/yaml_legacy.rs (FrontMatter/StoryMetadata structs, parse_front_matter,
  set_front_matter_field, yaml_residue marker) — file deleted.
- ItemMeta::from_yaml — deleted; callers pass typed ItemMeta::named(...) or
  ItemMeta::default() and use typed CRDT setters (set_depends_on,
  set_blocked, set_retry_count, set_agent, set_qa_mode, set_review_hold,
  set_item_type, set_epic, set_mergemaster_attempted) for the rest.
- write_coverage_baseline_to_story_file + read_coverage_percent_from_json —
  the coverage_baseline YAML field was write-only (nothing read it back);
  removed along with its caller in agent_tools/lifecycle.rs.
- update_story_in_file's generic `front_matter` HashMap parameter —
  tool_update_story now intercepts every known field name and routes it
  to a typed CRDT setter; unknown keys are rejected with an explicit error
  pointing at the typed setters. The function only takes user_story /
  description sections now.
- All 117 ItemMeta::from_yaml callsites migrated. Where tests previously
  passed a YAML-shaped content blob and relied on the helper to extract
  name/depends_on/blocked/agent/qa, they now pass:
    write_item_with_content(id, stage, content, ItemMeta::named("Foo"))
    crate::crdt_state::set_depends_on(id, &[...])    // when needed
    crate::crdt_state::set_blocked(id, true)         // when needed
    crate::crdt_state::set_agent(id, Some("..."))    // when needed
- write_story_content + write_story_file (test helper) now take an
  explicit `name: Option<&str>` instead of parsing it from content.
- db::ops::move_item_stage stopped re-parsing YAML on every stage
  transition; metadata is read straight from the CRDT view when mirroring
  the row into SQLite.

New CRDT setters added for symmetry:
- crdt_state::set_name (mirrors set_agent — explicit name updates).

cargo fmt --check, clippy --all-targets -- -D warnings, and the
2830-test suite all pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/src/service/notifications/io/tests_notifications.rs

@@ -18,7 +18,7 @@ async fn rate_limit_warning_sends_notification_with_agent_and_story() {
         "365_story_rate_limit",
         "2_current",
         "---\nname: Rate Limit Test Story\n---\n",
-        crate::db::ItemMeta::from_yaml("---\nname: Rate Limit Test Story\n---\n"),
+        crate::db::ItemMeta::named("Rate Limit Test Story"),
     );
 
     let (watcher_tx, watcher_rx) = broadcast::channel::<WatcherEvent>(16);
@@ -145,7 +145,7 @@ async fn story_blocked_sends_notification_with_reason() {
         "425_story_blocking_test",
         "2_current",
         "---\nname: Blocking Test Story\n---\n",
-        crate::db::ItemMeta::from_yaml("---\nname: Blocking Test Story\n---\n"),
+        crate::db::ItemMeta::named("Blocking Test Story"),
     );
 
     let (watcher_tx, watcher_rx) = broadcast::channel::<WatcherEvent>(16);

server/src/service/notifications/io/tests_stage.rs

@@ -21,7 +21,7 @@ async fn stage_notification_uses_dynamic_room_ids() {
         "10_story_foo",
         "3_qa",
         "---\nname: Foo Story\n---\n",
-        crate::db::ItemMeta::from_yaml("---\nname: Foo Story\n---\n"),
+        crate::db::ItemMeta::named("Foo Story"),
     );
 
     let (watcher_tx, watcher_rx) = broadcast::channel::<WatcherEvent>(16);
@@ -111,7 +111,7 @@ fn read_story_name_reads_from_front_matter() {
         "9942_story_my_feature",
         "2_current",
         "---\nname: My Cool Feature\n---\n# Story\n",
-        crate::db::ItemMeta::from_yaml("---\nname: My Cool Feature\n---\n# Story\n"),
+        crate::db::ItemMeta::named("My Cool Feature"),
     );
 
     let tmp = tempfile::tempdir().unwrap();
@@ -134,7 +134,7 @@ fn read_story_name_returns_none_for_missing_name_field() {
         "9943_story_no_name",
         "2_current",
         "---\ncoverage_baseline: 50%\n---\n# Story\n",
-        crate::db::ItemMeta::from_yaml("---\ncoverage_baseline: 50%\n---\n# Story\n"),
+        crate::db::ItemMeta::default(),
     );
 
     let tmp = tempfile::tempdir().unwrap();