feat(1001): recover_half_written_items MCP tool

Adds db::recover, a discovery + recovery layer for pipeline items that
got half-written before the Stage 1 fix landed (content in content
store + SQLite shadow, no live CRDT entry). For each orphan, the
content body is re-anchored to a fresh non-tombstoned id and the old
id's content row is cleared.

Exposed as the recover_half_written_items MCP tool. dry_run defaults
to true so the caller can review what would change before mutating.

YAML front-matter parsing is hand-rolled and scoped to the three
fields the create_*_file path emits (name, type, depends_on). It
tolerates missing or malformed lines by falling back to safe
defaults; the orphan is recovered with the best metadata we can pull
from the body and the rest is left to the operator to fix up.

The discovery step is read-only and idempotent. Recovery is also
idempotent in the sense that once an orphan is lifted, the next
discovery pass won't see it.

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

server/src/db/mod.rs

@@ -17,11 +17,14 @@
 pub mod content_store;
 /// Write operations for the pipeline — content, stage transitions, and deletions.
 pub mod ops;
+/// Recovery for half-written pipeline items (bug 1001 backfill).
+pub mod recover;
 /// Background shadow-write task — persists pipeline items to SQLite asynchronously.
 pub mod shadow_write;
 
 pub use content_store::{ContentKey, all_content_ids, delete_content, read_content, write_content};
 pub use ops::{ItemMeta, delete_item, move_item_stage, next_item_number, write_item_with_content};
+pub use recover::{find_half_written_items, recover_half_written_items};
 pub use shadow_write::init;
 
 #[cfg(test)]