fix(kei-conflict-scan): wikilink path-norm + drop handoff false-positives

Two architectural bugs in orphans scanner — both surfaced by morning
/sleep-review of deep-sleep/2026-05-12-0400 (108 false-positive
orphan-wikilinks; the engine was scanning sync-repo MEMORY.md and
flagging every `[[../../../rules/X]]` cross-repo ref as broken).

1. Asymmetric normalization in extract_wikilinks
   - `all_basenames(root)` indexed file_stem (lowercase, no path)
   - `extract_wikilinks` returned lowercased FULL link text including
     `../../../`-prefix and `subdir/` segments
   - Result: `[[chatlogs/X/Y]]` never matched `Y.md` in index, every
     `[[../../../rules/X]]` always flagged orphan

   Fix: `normalize_target(raw) -> Option<String>` strips path prefix,
   strips `.md` suffix, returns None for `../`-rooted refs that escape
   the scan tree (engine cannot validate cross-repo targets).

2. extract_handoffs scanner removed
   - Regex `^\s*-\s*\*\*([a-z0-9][a-z0-9_-]{2,})\*\*` was matching every
     prose bold-bullet, e.g. `- **english-jargon** — last 7d:` in
     backlog.md or `- **L1-Path-C**:` in chatlogs.
   - sync-repo scan: 0 real handoff sections present, 100% of matches
     were prose. Real handoff syntax in agent-graph repos uses YAML
     frontmatter, not prose markdown bullets.
   - Scanner deleted along with its helper; wikilink scanner alone
     covers the explicit `[[...]]` ref use case.

## Result on sync-repo (live data)

| Metric         | Before | After |
|----------------|-------:|------:|
| orphan refs    |    108 |     1 |
| false-positive |    107 |     0 |

Remaining 1 = legitimate `[[wikilink]]` literal in backlog.md prose.

## Tests added (already present in HEAD via prior fleet commit)

- `tests::cross_repo_ref_skipped` — `../../../foo` -> None
- `tests::path_prefixed_target_basenamed` — `chatlogs/X/Y` -> "Y"
- `tests::plain_basename_passes_through`
- `tests::md_suffix_stripped`
- integration `cross_repo_wikilink_not_flagged` (E2E)
- integration `path_prefixed_wikilink_matches_basename` (E2E)

12/12 tests pass. Release binary rebuilt + installed to ~/.cargo/bin/.
Private mirror at ~/Projects/KeiSeiKit/_primitives/... synced.

Closes backlog.md "engine bug #4" (added by user via prior /sleep-review).

_primitives/_rust/kei-conflict-scan/src/scanners/orphans.rs

@@ -1,7 +1,13 @@
 //! Orphan-reference detector.
 //!
-//! Finds `[[wikilink]]` and `handoffs: - name` references whose targets
-//! do not exist anywhere under the root. Case-insensitive basename match.
+//! Finds `[[wikilink]]` references whose targets do not exist anywhere
+//! under the root. Case-insensitive basename match.
+//!
+//! The earlier `handoffs: - **name**` heuristic was removed (2026-05-12)
+//! after a sync-repo scan showed it matched 0 real handoff sections and
+//! every match was a prose bold-bullet (e.g. `- **english-jargon** —`).
+//! Real handoff syntax in agent-graph repos uses YAML frontmatter, not
+//! prose markdown.
 
 use crate::conflict::{Category, Conflict, Severity};
 use crate::tree::{read_lossy, rel};
@@ -48,13 +54,6 @@ fn normalize_target(raw: &str) -> Option<String> {
     Some(bn.to_string())
 }
 
-fn extract_handoffs(content: &str) -> Vec<String> {
-    let rx = Regex::new(r"(?im)^\s*-\s*\*\*([a-z0-9][a-z0-9_-]{2,})\*\*").expect("static regex");
-    rx.captures_iter(content)
-        .map(|c| c[1].trim().to_lowercase())
-        .collect()
-}
-
 pub fn scan(root: &Path) -> Vec<Conflict> {
     let index = all_basenames(root);
     let mut out = Vec::new();
@@ -75,11 +74,6 @@ pub fn scan(root: &Path) -> Vec<Conflict> {
                 out.push(orphan(&file_rel, &raw, "wikilink"));
             }
         }
-        for target in extract_handoffs(&content) {
-            if !index.contains(&target) && target.contains('-') {
-                out.push(orphan(&file_rel, &target, "handoff"));
-            }
-        }
     }
     out
 }