wip(929): stage 1 — migrate chat/commands/* off yaml_legacy

Each chat command that previously read parse_front_matter for story
metadata (name, agent, depends_on, blocked, retry_count, merge_failure,
qa_mode) now reads from the typed CRDT API:

- WorkItem (via crdt_state::read_item) for pipeline-item registers.
- MergeJobView (via crdt_state::read_merge_job) for the merge failure
  detail text, which has its own LWW-map CRDT entry.

Files migrated: depends.rs, freeze.rs, move_story.rs, overview.rs,
status/render.rs, triage.rs, unblock.rs, unreleased.rs.

unblock.rs: also removes the legacy front-matter cleanup branch that
fired when the typed Blocked→Coding transition failed. Post-929 there
is no YAML on disk to clean; the fallback now just resets retry_count
in the CRDT.

triage.rs: drops the YAML-only `review_hold` and `coverage_baseline`
fields from the dump. These have no CRDT register and were never
load-bearing on the triage output; if needed later, add a CRDT register
and surface it back.

Tests:
- The three status/render merge-failure rendering tests now seed a
  MergeJob CRDT entry via write_merge_job instead of writing YAML.
- The unblock test that asserted YAML cleanup on disk is now an assertion
  on the CRDT registers (blocked=false, retry_count=0). Also re-seeded
  in `2_blocked` stage so the typed Blocked → Coding transition actually
  fires (not the fallback path).

All 2855 tests pass; fmt clean; clippy clean.

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

server/src/chat/commands/overview.rs

@@ -105,13 +105,11 @@ fn find_story_merge_commit(root: &std::path::Path, num_str: &str) -> Option<Stri
     if hash.is_empty() { None } else { Some(hash) }
 }
 
-/// Find the human-readable name of a story by searching CRDT then content store.
+/// Find the human-readable name of a story from the CRDT name register
+/// (story 929 — CRDT is the sole source of story metadata).
 fn find_story_name(root: &std::path::Path, num_str: &str) -> Option<String> {
-    let (_, _, _, content) = crate::chat::lookup::find_story_by_number(root, num_str)?;
-    let content = content?;
-    crate::db::yaml_legacy::parse_front_matter(&content)
-        .ok()
-        .and_then(|m| m.name)
+    let (story_id, _, _, _) = crate::chat::lookup::find_story_by_number(root, num_str)?;
+    crate::crdt_state::read_item(&story_id).and_then(|w| w.name().map(str::to_string))
 }
 
 /// Return the `git show --stat` output for a commit.