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/http/workflow/utils.rs

@@ -11,19 +11,23 @@ pub(crate) fn read_story_content(_project_root: &Path, story_id: &str) -> Result
 }
 
 /// Write story content to the DB content store and CRDT.
+///
+/// Pass `Some(name)` when creating a new item or renaming an existing one,
+/// `None` to leave the existing name register untouched.  The CRDT is the
+/// single source of truth for every metadata field — callers must use the
+/// typed setters (`crdt_state::set_depends_on`, `set_item_type`, …) for
+/// anything beyond name.
 pub(crate) fn write_story_content(
     _project_root: &Path,
     story_id: &str,
     stage: &str,
     content: &str,
+    name: Option<&str>,
 ) {
-    let mut meta = crate::db::ItemMeta::from_yaml(content);
-    // CRDT is the single source of truth for depends_on.  Never overwrite the
-    // register from YAML here — the typed setter (crdt_state::set_depends_on)
-    // is the only authorised write path.  Passing None leaves the existing
-    // register untouched on update and initialises new items to "" so the
-    // explicit set_depends_on call in each create function takes effect.
-    meta.depends_on = None;
+    let meta = crate::db::ItemMeta {
+        name: name.map(str::to_string),
+        ..Default::default()
+    };
     crate::db::write_item_with_content(story_id, stage, content, meta);
 }
 
@@ -273,7 +277,7 @@ mod tests {
             "9877_story_foo",
             "1_backlog",
             "---\nname: Foo\n---\n",
-            crate::db::ItemMeta::from_yaml("---\nname: Foo\n---\n"),
+            crate::db::ItemMeta::named("Foo"),
         );
         let tmp = tempfile::tempdir().unwrap();
         assert!(next_item_number(tmp.path()).unwrap() >= 9878);