wip(929): stage 5 — drop FS-based dep checks and qa-mode parser from io/story_metadata

Migrate the last three callers of the FS-scanning dependency helpers to the
CRDT-direct equivalents and delete the dead helpers:

- agents/pool/auto_assign/story_checks.rs: has_unmet_dependencies and
  check_archived_dependencies now wrap check_unmet_deps_crdt /
  check_archived_deps_crdt directly. Tests rewritten to seed the CRDT.
- http/mcp/story_tools/story/update.rs: bug-503 archived-dep warning now
  reads from CRDT instead of scanning 6_archived.
- agents/pool/pipeline/advance/helpers.rs: resolve_qa_mode_from_store is
  CRDT-only (the FS fallback for content-store-empty stories is gone).
- io/story_metadata/parser.rs: resolve_qa_mode_from_content removed.
- io/story_metadata/deps.rs: check_unmet_deps and dep_is_done deleted,
  along with the unused check_unmet_deps_from_list helper.
- io/story_metadata/mod.rs: re-exports trimmed accordingly.

check_archived_deps_from_list survives because story-creation still calls
it before the CRDT entry exists (used from story_tools/story/create.rs).

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

server/src/io/story_metadata/parser.rs

@@ -29,16 +29,6 @@ pub fn resolve_qa_mode(story_id: &str, default: QaMode) -> QaMode {
         .unwrap_or(default)
 }
 
-/// Resolve the effective QA mode by parsing legacy YAML front matter from a
-/// markdown body.  Used during one-time fallbacks when the CRDT register isn't
-/// set; new code should always read `qa_mode` from the CRDT.
-pub fn resolve_qa_mode_from_content(_story_id: &str, content: &str, default: QaMode) -> QaMode {
-    crate::db::yaml_legacy::parse_front_matter(content)
-        .ok()
-        .and_then(|m| m.qa)
-        .unwrap_or(default)
-}
-
 /// Return `true` if the story is in the `Frozen` pipeline stage.
 ///
 /// Checks the typed CRDT stage via `read_typed`. Used by the pipeline advance