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/freeze.rs

@@ -4,7 +4,6 @@
 //! advancement and auto-assign until `unfreeze <number>` restores the prior stage.
 
 use super::CommandContext;
-use crate::db::yaml_legacy::parse_front_matter;
 use std::path::Path;
 
 /// Handle the `freeze` command.
@@ -93,15 +92,13 @@ fn unfreeze_by_story_id(story_id: &str) -> String {
     }
 }
 
-/// Look up the display name for a story by reading its content store entry.
+/// Look up the display name for a story from the CRDT name register
+/// (story 929 — CRDT is the sole source of story metadata).
 ///
-/// Falls back to `story_id` if the content is missing or the front matter
-/// cannot be parsed.
+/// Falls back to `story_id` if no CRDT entry exists.
 fn resolve_story_name(story_id: &str) -> String {
-    crate::db::read_content(story_id)
-        .as_deref()
-        .and_then(|c| parse_front_matter(c).ok())
-        .and_then(|m| m.name)
+    crate::crdt_state::read_item(story_id)
+        .and_then(|w| w.name().map(str::to_string))
         .unwrap_or_else(|| story_id.to_string())
 }