feat(tui): AI provider tab + expanded General settings

Add a dedicated AI tab with provider Select, model Input, base URL Input,
and masked API key Input (write-only, stored in vault). Switching providers
reactively updates the model placeholder, base URL default, and shows/hides
the API key row for cloud vs. local providers. ctrl+s saves config and vault.

Extend GENERAL_FIELDS with Memory, Security, Plugin, and Daemon sections
using a new "section" header type and optional int cast for numeric fields.
_CoreField gains cast: type | None for automatic value coercion on save.

Add 5 new tests covering AI tab rendering, config save, vault key write,
vault key skip-on-empty, and section header rendering.

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

tests/unit/test_config_tui.py

@@ -1,7 +1,7 @@
 import json
 from unittest.mock import patch
 
-from textual.widgets import DataTable, Input, Switch, TabbedContent
+from textual.widgets import DataTable, Input, Label, Select, Switch, TabbedContent
 
 from pyra.config.schema import ProviderConfig, PyraConfig
 
@@ -68,7 +68,7 @@ def test_general_fields_non_empty():
 def test_general_fields_all_valid_types():
     from pyra.config.tui import GENERAL_FIELDS
 
-    valid_types = {"text", "bool", "select"}
+    valid_types = {"text", "bool", "select", "section"}
     for f in GENERAL_FIELDS:
         assert f.type in valid_types, f"Field '{f.path}' has unexpected type '{f.type}'"
 
@@ -82,6 +82,8 @@ async def test_config_app_renders_all_general_fields(tmp_pyra_home):
     save_config(_make_cfg())
     async with ConfigApp().run_test() as pilot:
         for f in GENERAL_FIELDS:
+            if f.type == "section":
+                continue
             wid = _fid(f.path)
             if f.type == "bool":
                 assert pilot.app.query_one(f"#{wid}", Switch)
@@ -150,8 +152,8 @@ async def test_plugin_config_tab_appears_for_plugin_with_config_fields(tmp_pyra_
         async with ConfigApp().run_test() as pilot:
             content = pilot.app.query_one(TabbedContent)
             tab_count = len(list(content.query("TabPane")))
-            # General + Plugins + fake plugin tab
-            assert tab_count == 3
+            # AI + General + Plugins + fake plugin tab
+            assert tab_count == 4
 
 
 async def test_q_key_exits_app(tmp_pyra_home):
@@ -162,3 +164,101 @@ async def test_q_key_exits_app(tmp_pyra_home):
     async with ConfigApp().run_test() as pilot:
         await pilot.press("q")
     # Reaching here means the app exited cleanly
+
+
+async def test_ai_tab_renders_provider_fields(tmp_pyra_home):
+    from pyra.config.manager import save_config
+    from pyra.config.tui import ConfigApp
+
+    save_config(_make_cfg())
+    async with ConfigApp().run_test() as pilot:
+        assert pilot.app.query_one("#ai-provider", Select)
+        assert pilot.app.query_one("#ai-model", Input)
+        assert pilot.app.query_one("#ai-base-url", Input)
+
+
+async def test_ai_tab_save_updates_config(tmp_pyra_home):
+    from textual.app import App as TextualApp, ComposeResult as CR
+
+    from pyra.config.manager import load_config, save_config as initial_save
+    from pyra.config.tui import _AITab
+
+    initial_save(_make_cfg())
+
+    class _TestApp(TextualApp):
+        def compose(self) -> CR:
+            yield _AITab()
+
+    saved = []
+    with patch("pyra.config.tui.save_config", side_effect=lambda c: saved.append(c) or None):
+        async with _TestApp().run_test() as pilot:
+            pilot.app.query_one("#ai-model", Input).value = "llama3:70b"
+            await pilot.pause()
+            await pilot.press("ctrl+s")
+
+    assert saved, "save_config was not called"
+    assert saved[-1].ai.model == "llama3:70b"
+
+
+async def test_ai_tab_save_calls_set_key_when_provided(tmp_pyra_home):
+    from textual.app import App as TextualApp, ComposeResult as CR
+
+    from pyra.config.manager import save_config as initial_save
+    from pyra.config.tui import _AITab
+
+    initial_save(_make_cfg())
+
+    class _TestApp(TextualApp):
+        def compose(self) -> CR:
+            yield _AITab()
+
+    calls = []
+    with patch("pyra.config.tui.save_config"):
+        with patch("pyra.config.tui.set_key", side_effect=lambda p, k: calls.append((p, k))):
+            async with _TestApp().run_test() as pilot:
+                pilot.app.query_one("#ai-key", Input).value = "sk-test"
+                await pilot.pause()
+                await pilot.press("ctrl+s")
+
+    assert calls, "set_key was not called"
+    assert calls[-1][1] == "sk-test"
+
+
+async def test_ai_tab_save_skips_set_key_when_empty(tmp_pyra_home):
+    from textual.app import App as TextualApp, ComposeResult as CR
+
+    from pyra.config.manager import save_config as initial_save
+    from pyra.config.tui import _AITab
+
+    initial_save(_make_cfg())
+
+    class _TestApp(TextualApp):
+        def compose(self) -> CR:
+            yield _AITab()
+
+    calls = []
+    with patch("pyra.config.tui.save_config"):
+        with patch("pyra.config.tui.set_key", side_effect=lambda p, k: calls.append((p, k))):
+            async with _TestApp().run_test() as pilot:
+                # Leave api-key empty (default)
+                await pilot.pause()
+                await pilot.press("ctrl+s")
+
+    assert not calls, "set_key should not be called when key input is empty"
+
+
+async def test_general_tab_renders_section_headers(tmp_pyra_home):
+    from textual.app import App as TextualApp, ComposeResult as CR
+
+    from pyra.config.manager import save_config as initial_save
+    from pyra.config.tui import _GeneralTab
+
+    initial_save(_make_cfg())
+
+    class _TestApp(TextualApp):
+        def compose(self) -> CR:
+            yield _GeneralTab()
+
+    async with _TestApp().run_test() as pilot:
+        headers = list(pilot.app.query(".section-header"))
+        assert len(headers) >= 5, "Expected at least 5 section headers"