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/status/render.rs

@@ -81,14 +81,15 @@ pub(crate) fn build_status_from_items(
         .unwrap_or_default()
         .into_iter()
         .collect();
+    // Merge-failure detail now lives on the typed MergeJob CRDT entry
+    // (story 929 — CRDT is the sole source of metadata).
     let merge_failures: HashMap<String, String> = items
         .iter()
         .filter(|i| matches!(i.stage, Stage::Merge { .. }))
         .filter_map(|i| {
-            let content = crate::db::read_content(&i.story_id.0)?;
-            let meta = crate::db::yaml_legacy::parse_front_matter(&content).ok()?;
-            let mf = meta.merge_failure?;
-            Some((i.story_id.0.clone(), mf))
+            let job = crate::crdt_state::read_merge_job(&i.story_id.0)?;
+            let err = job.error?;
+            Some((i.story_id.0.clone(), err))
         })
         .collect();