docs(skills): point pi sections to OpeItcLoc03/pi-extensions repo

source of truth for the three pi extensions moved from .common/lib/pi-extensions
(dev-copies) to the new pi-extensions repo; deploy via just install. Updated:
session-inbox-monitor §Pi, session-handoff Headless(pi), vision-subagent
+ realization section. Cross-link AC#5.

skills/session-inbox-monitor/SKILL.md

@@ -138,8 +138,9 @@ other projects' inboxes (vitya's rule: an agent may only read its own
 directory's inbox). Installed globally so *every* pi session has the
 capability, but each session only ever touches its own project's inbox.
 
-- **Source of truth:** `.common/lib/pi-extensions/inbox-monitor.ts` (Node
-  built-ins only, no npm deps). Deploy: copy to
+- **Source of truth:** `~/projects/pi-extensions/extensions/inbox-monitor.ts`
+  (репо `OpeItcLoc03/pi-extensions`, Gitea — дом pi-расширений). Deploy:
+  `just install` в клоне репо — копирует с затираанием в
   `~/.pi/agent/extensions/inbox-monitor.ts` (global → every pi, every
   directory), hot-reload with `/reload`. Test:
   `node --experimental-strip-types .common/lib/pi-extensions/inbox-monitor.test.mjs`