intro-video RE: deep demux-core instrumentation + handoff hygiene

Investigation probes for the ADV.wmv intro-video deadlock (feeder's demux
source-read 0x825211a0 returns no-data 0x80500000 where canary returns 0).

- xenia-kernel/state.rs: extend AUDIT-DEREF (fire_audit_pc_probe_if_match) to
  deep-dump the demux-state object (to +0xfc), its buffer descriptor [sub+4],
  the byte-source sub-objects ([sub+0]/[+0x30]/[+0x94] and [src0+0x2c]), and
  to WALK the windowed-buffer cached-block linked list (AUDIT-BLK: per-block
  64-bit start/size/dataptr) exactly as mapper 0x82522118 does. Read-only,
  env-gated (XENIA_AUDIT_DEREF); lockstep digest unaffected.
- xenia-app/main.rs: XENIA_DUMP_SLOTS observe-only scheduler runqueue dump.
- xenia-app/tests/sylpheed_oracles.rs: resolve ISO via SYLPHEED_ISO, then the
  repo-root sylpheed.iso symlink, then default; fix path typo.
- .gitignore: exclude .claude/ (71k files / 66GB agent worktrees) and the
  local investigation artifacts (audit-runs/, exit-thread-state.json, zq_*.py).

Findings (full chain in handoff notes): all ASF header metadata parses
correctly (packet size 16415, count 4728, 2 streams); cursors correct
(cur=5868, limit=77.6M); the windowed buffer works and slides (512B blocks);
no-data originates deep in the byte-read/parse chain, not from an empty buffer.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -3,9 +3,17 @@ target/
 *.xiso
 *.db
 
+# Claude Code project data: transcripts, subagent logs, and (huge) agent git
+# worktrees. ~71k files / 66 GB — must never be scanned by git or the editor.
+.claude/
+
 # Audit reports / pre-pass findings (local artifacts, not source)
 audit-out/
 audit-*.md
+audit-runs/
+exit-thread-state.json
+zq_dis.py
+zq_fn.py
 
 # Run logs from stress harnesses and ad-hoc captures
 *.stdout