Add settings page, model management, and chat UX improvements

- Settings infrastructure: key-value settings table, GET/PUT API, Pinia store
- Configurable assistant name (default "Fable") in settings and LLM system prompt
- Model catalog with 18 models in 3 categories (General Purpose, Coding,
  Uncensored / Creative Writing) with download/select/remove functionality
- Move Ollama status indicator from chat views to global nav bar
- Chat bubble layout: user messages right-aligned, assistant left-aligned
- Floating dark input bar with auto-focus and circular send button
- Fix HTML entity rendering (' apostrophe issue in marked/DOMPurify pipeline)
- Fix new chat button navigation (fetchConversation before router.push)
- Recent chats section on home page with "New Chat" button
- Update summary.md with Phase 4.5 changes

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

alembic/versions/0006_add_settings_table.py

@@ -0,0 +1,28 @@
+"""add settings table
+
+Revision ID: 0006
+Revises: 0005
+Create Date: 2025-01-01 00:00:00.000000
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+revision = "0006"
+down_revision = "0005"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    conn = op.get_bind()
+    conn.execute(sa.text("""
+        CREATE TABLE IF NOT EXISTS settings (
+            key TEXT PRIMARY KEY,
+            value TEXT NOT NULL DEFAULT ''
+        )
+    """))
+
+
+def downgrade() -> None:
+    op.execute("DROP TABLE IF EXISTS settings")