v7.2.1

Rolls up everything merged since v7.2.0 plus a full overhaul of the project's contributor-facing documentation.

## ✨ Highlights

### 📞 Deferred transfer handoff routing (#479/#480)
Transfers no longer cut off the assistant's spoken handoff. The new `tools.transfer.defer_until_playback_complete` setting waits for handoff audio to finish draining, and the default `predial_then_bridge` strategy dials the destination *while* the caller hears the message, then bridges — no dead air, no clipped goodbyes. Works across blind, live-agent, and attended transfers for extensions, queues, and ring groups; `cancel_transfer` can still cancel before commit. Configurable from the Tools UI.

### 🔄 First-class UI-driven updater
The Admin UI's Updates page now discovers stable/main/custom-branch updates, previews changed files and service impact, builds the updater with visible progress, streams job logs, keeps run history, and offers rollback/copy-recovery for failures — including post-update validation failures.

### 🩹 Fixes
- **"Restart required" banner is now server-driven** — no more stale banners after out-of-band restarts; it shows only when a restart is genuinely needed (#478)
- **Call History no longer logs non-AVA PBX channels** as zero-duration "Unknown" abandoned calls (#490/#492)
- **Agent dialplan copy works without the modern Clipboard API** — hidden-textarea fallback shared with Call Scheduling (#491/#493)
- **HTTP tool modal** no longer hides add-row actions or silently drops draft fields (#494/#495)
- **Windows CLI build restored** — `agent update`'s file lock and self-update re-exec now use platform-specific implementations, and CI cross-compiles all five release targets on every PR (#501)

## 📚 Docs & contributor experience overhaul (#500)

- **`AVA.mdc` rewritten** as a self-contained AI-assistant context file — load it into Claude, Cursor, Windsurf, Codex, or Copilot and your assistant gets the project map, the v7 Agents architecture, engineering guardrails, and the PR workflow. Reviewed for drift every release.
- **Contributor funnel repaired**: dead guide links, phantom setup script, and stale branch instructions replaced with working, committed docs; one-branch-per-PR now documented.
- **Honest support policy**: `SECURITY.md` now commits to the two most recent minor trains (currently 7.2.x and 7.1.x) instead of nine trains with "TBD" dates.
- **Feature maturity labels** in the README: Outbound Calling is `Alpha`; FS-PBX and ViciDial guides are `Community`.
- `AI_AGENT` documented as the preferred per-call dialplan selector (`AI_CONTEXT` remains supported as legacy).

## ⬆️ Upgrading

Standard upgrade — no migration steps, no config changes required.

```bash
git fetch --tags && git checkout v7.2.1
docker compose build admin_ui && docker compose up -d
```

Or use the Admin UI's Updates page.

**Full changelog**: https://github.com/hkjarral/AVA-AI-Voice-Agent-for-Asterisk/blob/main/CHANGELOG.md

Thanks to everyone who reported issues and tested fixes — and to @foytech for the production feedback driving the per-agent voice work landing in v7.3.0.