fix(auth): Google Sign-In audience mismatch + remove per-user accent color

Root cause of "Google authentication failed": appsettings.Development.json
had Auth:GoogleClientId set to the literal placeholder
"CHANGE_ME_GOOGLE_CLIENT_ID" while the frontend's .env.development had a
real (already-public, already-committed) client ID -- every Google ID
token's audience check failed against the backend's placeholder. Fixed
by setting the same real client ID on both sides (a client ID is a
public identifier, not a secret, safe to commit -- unlike a client
secret). Also enabled Auth:AllowRegistration in dev so the existing
Google-first self-serve-signup path (auto-create on unmatched verified
email, auto-link on matching verified email -- built during Wave 7) is
actually exercisable locally.

Wired the previously-missing Auth__MicrosoftClientId /
NEXT_PUBLIC_MICROSOFT_CLIENT_ID into docker-compose.yml/.env.example
(distinct from the existing MICROSOFT_CLIENT_ID used for Outlook mail
linking) -- Microsoft sign-in was never deployable, a leftover gap from
when it was built. Fixed a stale env-var name in the Microsoft setup
hint copy (still said REACT_APP_*, predates the Next.js migration).

Removed the per-user accent color picker entirely: it was purely
client-side (localStorage + theme.ts), never touched the backend/DB.
theme.ts now hardcodes a single ACCENT constant; themePrefs.ts drops
get/set/clearAccentColor; App.tsx and SettingsView.tsx drop the
accentColor prop threading. Dead accent-related i18n keys removed from
both locales.

Consolidated Settings' "Account" tab (duplicated GoogleAuthCard, which
already lives on the Profile page) into Profile: moved AuthStatusCard
and EmailProviderConnections there alongside the existing Google/
Microsoft auth cards, so identity/account-linking lives in one place.
Settings drops from 5 tabs to 4 and its General tab uses a consistent
SectionCard layout instead of ad-hoc per-card styling.

Verified: dotnet build/test (177/177) and npm build/test (57/57) both
green; confirmed live against a running dev server that /auth/config
now reports googleEnabled with the corrected client ID, Settings has
no accent controls, and Profile shows the consolidated auth section.

docker-compose.yml

@@ -19,8 +19,9 @@ services:
       - Auth__JwtKey=${AUTH_JWT_KEY}
       - Auth__AdminEmail=${AUTH_ADMIN_EMAIL}
       - Auth__AdminPassword=${AUTH_ADMIN_PASSWORD}
-      # Optional: allow Google ID-token bearer auth
+      # Optional: allow Google / Microsoft ID-token bearer auth (sign-in, not mail access)
       - Auth__GoogleClientId=${AUTH_GOOGLE_CLIENT_ID}
+      - Auth__MicrosoftClientId=${AUTH_MICROSOFT_CLIENT_ID}
       - Google__GmailClientSecret=${GOOGLE_GMAIL_CLIENT_SECRET}
       - Google__GmailRedirectUri=${GOOGLE_GMAIL_REDIRECT_URI}
       # Optional: Outlook / Microsoft 365 mail linking via Microsoft Graph
@@ -64,6 +65,7 @@ services:
       shm_size: '1gb'
       args:
         - NEXT_PUBLIC_GOOGLE_CLIENT_ID=${AUTH_GOOGLE_CLIENT_ID}
+        - NEXT_PUBLIC_MICROSOFT_CLIENT_ID=${AUTH_MICROSOFT_CLIENT_ID}
         # Optional override; default in production is `/api`
         - NEXT_PUBLIC_API_BASE_URL=${REACT_APP_API_BASE_URL}
     ports: