fix(linear): annotate circuit breaker globals so ty doesn't narrow

`ty check` infers `_consecutive_auth_failures = 0` as `Literal[0]` and
`_auth_circuit_open = False` as `Literal[False]`, which then rejects
the legitimate runtime flips (and the test fixture that resets them
between cases). Adding explicit `int` / `bool` annotations widens the
inferred type and fixes the CI typecheck failure introduced in
`f4633be`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: bgagent

agent/src/linear_reactions.py

@@ -98,8 +98,11 @@
 #: 2xx response resets the counter. The lock guards the read-modify-write
 #: against the daemon sweep thread.
 _AUTH_FAILURE_THRESHOLD = 3
-_consecutive_auth_failures = 0
-_auth_circuit_open = False
+# Annotated explicitly so ty doesn't narrow the initial values to
+# `Literal[0]` / `Literal[False]` — that narrowing would reject the
+# legitimate flips below (and any test that resets them).
+_consecutive_auth_failures: int = 0
+_auth_circuit_open: bool = False
 _auth_state_lock = threading.Lock()