offload-audit: require --note for filing: unavailable, now that it exists

Closes FR-6.4's wiki half — the reason reaches Audits/<target>/<date> instead
of living only in filing-plan's output. Also records the wiki_write
delete-by-sub_url gotcha.

skills/offload-audit/SKILL.md

@@ -176,7 +176,9 @@ runs **even when path A was skipped**.
 
 ```bash
 $IA/bin/audit-snapshot write --target <name> --from inv.json scan.json \
-    --classified classified.json --issue-map issue-map.json --repo <owner/repo>
+    --classified classified.json --issue-map issue-map.json \
+    --repo <owner/repo> \
+    --note "<anything the scripts cannot see — see below>"
 $IA/bin/audit-snapshot pages --target <name> > pages.json
 ```
 
@@ -187,9 +189,20 @@ each page in `pages.json` to `cluster:gitea-agent` for the wiki of
 `kotkan/claude-plugin-inference-arbitrage`, respecting `append_only` on the
 JSONL.
 
-When filing was unavailable, say so on the page: pass the reason through
-`audit-snapshot write --note "<reason>"` if that flag exists, and state it in
-the report regardless.
+`--note` is repeatable and is how a filing outcome reaches the page — the
+snapshot scripts make no Gitea calls and cannot see one. **When filing was
+unavailable, that note is required** (FR-6.4):
+
+```text
+--note "filing: unavailable — <the reason from filing-plan, verbatim>"
+```
+
+Use it likewise for a search that failed, or a plan you could not fully execute.
+Say it in the report either way; the note is what makes it durable.
+
+Publishing gotcha: `wiki_write` `create`/`update` take the page **title**, but
+`delete` takes the URL-decoded `sub_url` (`Data/<target>/snapshots.jsonl.-`) —
+deleting by title 404s.
 
 ## 7. Report to the user