feat(login): /login opens the provider picker with green connected badges

/login previously fired the resolved method's flow immediately — there was
no way to see providers or their status. It now lands on the provider
picker; already-connected providers show a green 'connected' badge in the
key column.

Shell: initialize() probes stored credentials once (primary session flag,
auth.json oauth/<provider> scopes, resolved platform keys env>auth.json>
config) and stamps _meta.connected on each advertised method
(connected_method_ids + stamp_connected_meta, pure and unit-tested).
Display state only — never an authorization input.

TUI:
- PendingMenuItem::connected() reads the badge from method meta; the
  picker renders it green (accent_success), replacing the shortcut hint.
- New Action::OpenLoginPicker: /login shows the picker; mid-session it
  stashes the view like dispatch_login, and starts no flow by itself.
- Mid-session picker: last row reads 'Cancel' and dispatches CancelLogin
  (clicking it must not exit the app); Esc also returns to the session.
- After a successful login, the just-authenticated method is stamped
  connected in the TUI's advertised-methods copy (auth_in_flight_method →
  AuthComplete), so a later /login shows the badge without re-initialize.

Verified: kigi-shell 5256 + kigi-tui 6870 tests green, clippy clean.

crates/codegen/kigi-tui/src/app/dispatch/router.rs

@@ -1,8 +1,8 @@
 //! Top-level action router: maps actions and action results to handlers.
 use super::auth::{
     dispatch_begin_platform_key_entry, dispatch_cancel_login, dispatch_cancel_platform_key_entry,
-    dispatch_login, dispatch_login_with, dispatch_logout, dispatch_submit_auth_code,
-    dispatch_submit_platform_api_key, dispatch_switch_account,
+    dispatch_login, dispatch_login_with, dispatch_logout, dispatch_open_login_picker,
+    dispatch_submit_auth_code, dispatch_submit_platform_api_key, dispatch_switch_account,
 };
 use super::ctx::{
     active_agent_session_id, get_active_agent_mut, navigate_clearing_selection,
@@ -877,6 +877,7 @@ pub(crate) fn dispatch(action: Action, app: &mut AppView) -> Vec<Effect> {
         }
         Action::Login => dispatch_login(app),
         Action::LoginWith(method_id) => dispatch_login_with(app, Some(method_id)),
+        Action::OpenLoginPicker => dispatch_open_login_picker(app),
         Action::CancelLogin => dispatch_cancel_login(app),
         Action::SubmitAuthCode(code) => dispatch_submit_auth_code(app, code),
         Action::BeginPlatformKeyEntry(target) => dispatch_begin_platform_key_entry(app, target),