provisioning: Linphone setup QR, "Set up a phone app"

GET /api/extensions/:id/softphone-qr (admin) and /api/me/softphone-qr
return {url, qr, expiresAt}: the link Linphone fetches and its QR as a
PNG data URL (qrcode), valid 24 h. Both are audited like revealing the
SIP password. JSON rather than a bare PNG, so the page can show the
link for desktop Linphone too.

The token is stateless per 07 §5: base64url(extensionId.expiry.hmac),
HMAC-SHA256 with APP_SECRET, checked timing-safe. /prov/linphone/
<token>.xml matches it before the other file names are lower-cased
(the token is case-sensitive); a bad or expired token is a 404 and a
counted failure. auth_info keys checked against liblinphone's config
reader; proxy keys stay (verify).

Web: a "Set up a phone app" section on My settings and in the admin
Credentials tab: Linphone with the QR, MicroSIP/Baresip by hand, and
the plain warning about mobile apps without push. e2e m10-t3: as a
user, the QR's link gives the XML and a baresip phone registers with
only what it holds.

Task: M10-T3

docs/spec/07-provisioning.md

@@ -205,6 +205,18 @@ Linphone provisioning:
 ```
 **(verify against Linphone's remote provisioning docs)**
 
+As built (M10-T3), `provisioning/linphone.ts`:
+- The `auth_info_0` keys (`username`, `passwd`, `domain`) match liblinphone's `AuthInfo` config
+  reader; the `proxy_0` keys are its classic names and stay **(verify)** until a phone scans it.
+- Both QR endpoints return JSON `{url, qr, expiresAt}` (`qr` = PNG data URL from `qrcode`), not a
+  bare PNG: the page shows the link too, for desktop Linphone. Each is in the audit log like
+  revealing the SIP password (the config carries it).
+- The token is case-sensitive, so `/prov/linphone/…` is matched before the other files are
+  lower-cased; a bad or expired token is a 404 and counts as a failure (07 §2 limits).
+  `provisioning.lanOnly` applies to it too: a mobile off the LAN can't fetch it then.
+- The display name's `"` becomes `'` in `reg_identity` (it sits inside a SIP quoted string).
+- "Set up a phone app" is a section of `/me/settings` and of the admin Credentials tab.
+
 Mobile limitation (state it plainly in the UI and admin guide): without push
 notifications, iOS and battery-optimized Android apps miss calls while in the
 background. A push gateway is a v2 item. For v1, recommend the desk phone + browser softphone,