fix(auth): login-flow provisioning — public login_url + session app passwords

Two fixes surfaced while testing Login Flow v2 provisioning behind a split
internal/external host (Docker: server↔Nextcloud over http://app, browser
over http://localhost:8080):

1. login_url pointed at the internal host. Nextcloud builds the login URL
   from the request host, so the browser-facing URL came back as
   http://app/login/v2/flow/... — unreachable from the user's browser. The
   poll endpoint was already rewritten to the internal host (correct, the
   server polls it); now LoginFlowV2Client also rewrites the login_url origin
   to settings.nextcloud_public_issuer_url when set (passed at all 5
   construction sites). When unset, behaviour is unchanged.

2. The app-password format guard rejected raw session tokens. core/
   getapppassword returns a long alphanumeric token, not the dashed 25-char
   Security-settings format, so the dashed-only regex 400'd the one-click
   opt-in handoff. Relax APP_PASSWORD_PATTERN to `^[a-zA-Z0-9-]{20,256}$`;
   the authoritative validation is still the BasicAuth check against Nextcloud.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/api/passwords.py

@@ -30,9 +30,11 @@ from ..http import nextcloud_httpx_client
 logger = logging.getLogger(__name__)
 
 # App password format regex (Nextcloud format: xxxxx-xxxxx-xxxxx-xxxxx-xxxxx)
-APP_PASSWORD_PATTERN = re.compile(
-    r"^[a-zA-Z0-9]{5}-[a-zA-Z0-9]{5}-[a-zA-Z0-9]{5}-[a-zA-Z0-9]{5}-[a-zA-Z0-9]{5}$"
-)
+# Shape guard only — the authoritative check is the BasicAuth validation
+# against Nextcloud below. Accepts both the dashed format a user copies from
+# Security settings (xxxxx-xxxxx-xxxxx-xxxxx-xxxxx) and the raw token returned
+# by the one-click ``core/getapppassword`` flow (a long alphanumeric string).
+APP_PASSWORD_PATTERN = re.compile(r"^[a-zA-Z0-9-]{20,256}$")
 
 # Timeout for Nextcloud API validation requests (seconds)
 NEXTCLOUD_VALIDATION_TIMEOUT = 10.0