Add customizable home dashboard with per-user pinned apps

- Users can pin/unpin any available service on their home page via a
  Customize mode; preferences persisted via PATCH /api/users/me/preferences
- Time-aware greeting renders the user's display name through React JSX
  (HTML-escaped by design — no dangerouslySetInnerHTML used)
- Added dashboard_app_ids JSON column to users table (migration c7e8f9a0b1d2)
- /settings now routes to a placeholder page

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/alembic/versions/c7e8f9a0b1d2_add_dashboard_app_ids_to_users.py

@@ -0,0 +1,28 @@
+"""add dashboard_app_ids to users
+
+Revision ID: c7e8f9a0b1d2
+Revises: a3f9c2d14e87
+Create Date: 2026-04-17 14:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision: str = 'c7e8f9a0b1d2'
+down_revision: Union[str, None] = 'a3f9c2d14e87'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        'users',
+        sa.Column('dashboard_app_ids', sa.JSON(), nullable=False, server_default='[]'),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column('users', 'dashboard_app_ids')