fix(issue-10,13): check every agy artifact for holders and purge orphaned leftovers

Round-3 review of f5a6575 (planner-reviewer-codex-01, R1/R2).

R1 - the adapter's in-use check handed only the conversation DB to lsof, so a
holder that keeps the presence lock (or a sidecar) open while naming the uuid
on no command line and in no session variable was invisible, and the held
lock was unlinked from under it. AgyAgentAdapter.conversation_in_use now
passes every path of the conversation (DB, -wal/-shm/-journal, brain,
annotation, presence lock).

R2 - both resolver stages required the DB, so once an interrupted or pre-#10
purge had removed it, the WAL/annotation/lock left behind were "no artifact"
(exit 5) forever. BaseAgentAdapter.has_artifacts (default: a uuid-bearing
artifact path that exists) replaces the resolver's path fallback, and agy's
override accepts any of its pieces.

Tests: a flock holder that names the uuid nowhere is refused and nothing is
removed; orphaned leftovers resolve to agy and are purged. VERSIONS.md
v4.4.3 items 1-2 and orc-onboard SKILL.md updated.

Refs #10 #13

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VCgu9Fa9iT7TbJUSzdq4Ff

.agents/skills/multi-agent-mux-orc-onboard/SKILL.md

@@ -45,7 +45,7 @@ Registers an orchestrator session UUID into the `orchestrator_uuids` list of `.m
 # residual: none (agent: agy)
 ```
 
-The purge runs before the registry update, so a refused purge (conversation in use, exit `5`) changes nothing. If no adapter finds an artifact for the UUID the registration is still removed with a warning. For agy the adapter also removes the SQLite sidecars (`-wal`/`-shm`/`-journal`), the title annotation and the presence lock (Issue #10) and reports anything under `~/.gemini/antigravity-cli` that still carries the UUID as `WARN residual:`.
+The purge runs before the registry update, so a refused purge (conversation in use, exit `5`) changes nothing. If no adapter finds an artifact for the UUID the registration is still removed with a warning. For agy the adapter also removes the SQLite sidecars (`-wal`/`-shm`/`-journal`), the title annotation and the presence lock (Issue #10) and reports anything under `~/.gemini/antigravity-cli` that still carries the UUID as `WARN residual:`. Orphaned leftovers — a WAL, annotation or lock whose DB is already gone — still resolve to agy and are purged, and the in-use check asks `lsof` about every one of those paths, so a holder that keeps only the presence lock open (naming the UUID nowhere) is refused too.
 
 ## Auto-Detection Hierarchy (Rev.2)