P2 cleanups: pin deps, prune job-run rows, unmask non-secret creds, enforce allowlist at login

- R11: pin requirements.txt to the versions running in the image, so a rebuild
  can't pull a breaking upstream release. Documented how to upgrade.
- R12: log rotation now also prunes job_runs rows older than 90 days (nulling
  the manual_imports FK reference first), so the table doesn't grow without
  bound. dedup/genre candidates are review state and left alone.
- U5: credential form shows non-secret fields (URLs, usernames, prefs) as plain
  text so they can be verified while typing; only real secrets stay masked.
  Dashboard IP card reworded from gluetun-specific to generic "Outbound IP".
- S9: enforce ALLOWED_EMAIL at the OIDC callback, before any user row or session
  is created, instead of only on later requests.

Verified: pinned build resolves; prune deletes only old rows and keeps the
manual_imports record; credentials page renders text+password inputs; a
disallowed email gets 403 with no user row, an allowed one succeeds.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/services/credential_service.py

@@ -44,6 +44,20 @@ SCOPE_DESCRIPTIONS = {
 CORE_SCOPES = {"spotify", "soulseek", "navidrome"}
 OPTIONAL_SCOPES = {"bandcamp", "azuracast", "qobuz", "telegram"}
 
+# The genuinely-secret fields, masked in the UI. Everything else is an
+# identifier, URL, or preference the user should be able to see while typing
+# so they can verify it (e.g. the Navidrome base URL or their Soulseek
+# username). Values are write-only either way -- never sent back to the browser.
+SECRET_KEYS = {
+    "client_secret",
+    "password",
+    "admin_pass",
+    "cookies_txt",
+    "api_key",
+    "token",
+    "bot_token",
+}
+
 
 def _upsert(db: Session, scope: str, key: str, value: str) -> None:
     row = db.execute(