Loki Mode

Fix: native/Keychain Claude login no longer misread as "not logged in"

• loki start no longer falsely blocks a genuinely logged-in user. The auth
  preflight assumed the Claude Code OAuth login always lives in
  ~/.claude/.credentials.json. That is false for the native Claude Code install
  (2.x on macOS), which stores the login in the macOS Keychain (service
  "Claude Code-credentials") and writes NO .credentials.json. A subscription
  user who was fully logged in was told "Claude Code is installed but not logged
  in -- the build would stall" and blocked from every build: the exact opposite
  of the zero-friction intent.

• The preflight now asks the CLI's own local auth-status first. A new
  _loki_claude_login_state() helper (autonomy/run.sh) prefers claude auth status (zero-network, ~0.2s, JSON "loggedIn"), which is authoritative for
  BOTH the file-based and the native/Keychain login, then falls back to the
  credentials file, then to a macOS Keychain existence check (existence only,
  never reading the secret, so it can never trigger a GUI keychain prompt that
  would hang a headless build). Critically it applies "inconclusive never
  false-fails" to auth: it hard-blocks ONLY on positive evidence of no login
  ("loggedout") or an expired token ("expired"); when the state cannot be proven
  ("unknown", e.g. an older CLI on a non-macOS box with no file) it fails OPEN
  and proceeds, so a real login is never blocked on uncertainty. claude login
  guidance and the LOKI_SKIP_AUTH_PREFLIGHT=1 / ANTHROPIC_API_KEY opt-outs
  are unchanged.

• A stale expired credentials file never overrides a live Keychain login.
  The native install can leave a now-expired ~/.claude/.credentials.json next
  to a valid Keychain login (it rotates the Keychain, not the file). The helper
  therefore checks the Keychain (a positive signal) BEFORE concluding "expired"
  from the file: a valid file -> logged in; else a Keychain entry -> logged in;
  only with neither is an expired file treated as genuinely expired. Genuine
  expiry (expired file, no Keychain) still returns "expired", so the 401-avoiding
  fast-fail is preserved.

• loki doctor now affirmatively confirms the login, on BOTH the bash and Bun
  routes. Both read claude auth status, so each shows "Claude CLI is logged in
  (subscription/OAuth login)" for a Keychain-backed login (previously the bash
  route fell through to a neutral "ANTHROPIC_API_KEY not set" line and the Bun
  route wrongly reported "login EXPIRED" for a Keychain login), warns on a genuine
  logged-out or expired state, and keeps the file-based expiry fallback for older
  CLIs. The bash<->Bun doctor output stays byte-identical (enforced by the
  bun-parity matrix).

• Regression coverage: tests/test-claude-login-state.sh extracts the real
  _loki_claude_login_state() helper from run.sh and drives every login state
  with fake claude AND security binaries on PATH (fully deterministic,
  independent of the machine's real login). The cases: auth-status logged in
  (no file); auth-status logged out; valid JSON with no explicit loggedIn
  boolean plus a valid file (must fall through to logged in, never a false hard
  block); valid file; expired file with no keychain (-> expired); expired file
  WITH a live keychain (-> logged in: the regression guard that a stale file
  never overrides a real Keychain login); keychain-only with no file; and the
  confident-logout path. Proves the exact user-reported scenario (logged in, no
  .credentials.json) no longer blocks.