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/http/mcp/story_tools/criteria.rs

@@ -13,9 +13,7 @@ use crate::http::workflow::{
     list_refactor_files, load_pipeline_state, load_upcoming_stories, remove_criterion_from_file,
     update_story_in_file, validate_story_dirs,
 };
-use crate::io::story_metadata::{
-    check_archived_deps, check_archived_deps_from_list, parse_unchecked_todos,
-};
+use crate::io::story_metadata::{check_archived_deps_from_list, parse_unchecked_todos};
 use crate::service::story::parse_test_cases;
 use crate::slog_warn;
 #[allow(unused_imports)]