feat(stockbit): one browser sign-in in idx-core for the CLI and MCP

`stockbit::signin` is now the single sign-in flow. `idx stockbit login`
waits on it in the foreground; the `stockbit_login` MCP tool runs it on a
thread and `stockbit_status` reports `sign_in.state`, so an agent knows when
to stop polling. Auto uses a browser unless the shell is over SSH or has no
display, and falls back to the local page only when the browser cannot start.

The browser way opens Stockbit's sign-in page in a profile only idx uses and
reads the session cookie over DevTools. What a real sign-in showed:

- The cookie is host-only on stockbit.com, so deleting by the assumed
  .stockbit.com removed nothing and left live tokens in the profile. It is
  now deleted by its own domain and path, with every other tab closed first,
  and read back to confirm.
- A signed-out page writes the cookie without tokens; it no longer counts.
- A profile belongs to one browser, so it records the executable that made it.
- On macOS the config directory depends on XDG_CONFIG_HOME, so a shell and an
  app started from the Dock disagreed; both default locations are now checked.
- A thread does not outlive main, so idx-mcp closes a waiting browser when
  stdin closes or on SIGTERM or Ctrl-C.

Progress goes to stderr, which keeps `-o json` to one document on stdout.

Google refused its own sign-in in this window on 2026-10-31, most likely over
the debugging flag; password sign-in works, and the docs and roadmap say so.

Claude-Session: https://claude.ai/code/session_01RqPPVaoFxLToGAXXBEoCtH

ROADMAP.md

@@ -14,10 +14,18 @@ history lives in git.
 - Multi-period financial statements (today `financials` is single-period)
 - Order book depth without a login: no free source exists (IDX sells delayed
   depth to vendors); `stocks orderbook` needs the user's Stockbit login.
-- Stockbit login follow-ups: a browser capture for `idx stockbit login`
-  (Chrome DevTools, as fzn0x/idx does) instead of pasting the cookie,
-  intraday OHLCV from the session's `1d` chart, and observing the session
-  API's open-market state name (assumed `STATE_NAME_MARKET_OPEN`).
+- Stockbit login follow-ups: intraday OHLCV from the session's `1d` chart;
+  observing the session API's open-market state name (assumed
+  `STATE_NAME_MARKET_OPEN`; `STATE_NAME_MARKET_CLOSED` seen 2026-10-29); an
+  opt-in daily refresh so a session outlives the refresh token's week, once
+  it is known whether Stockbit caps a session's total life; and the sign-in
+  response (`/login/v6/*`, read over DevTools' `Fetch`) as a second signal
+  beside the `credentialStorage` cookie, should Stockbit rename or move it.
+- Google sign-in in idx's browser window: Google refused it on 2026-10-31,
+  most likely over `--remote-debugging-port`. First confirm by trying Google
+  in a plain window on a throwaway profile; if that works, sign in with no
+  debugging flag and reopen the profile with it, on a blank page, to read the
+  cookie.
 - Observe Stockbit's `market_hour.status` in the pre-open (08:45-09:00) and
   the closing auction (15:50-16:00) before `--watch` or alerts build on it;
   `open`, `break` and `close` are known, and the bid/offer gate hides the book