feat: implement OpsBridge CLI (BRIDGE-WP-0001)

Full TDD implementation of the `bridge` CLI tool covering all phases
from BRIDGE-WP-0001: project scaffolding, config loading, state
management, audit logging, health checks, tunnel lifecycle manager, and
all CLI commands (up/down/restart/status/logs). 77 tests, all green.

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

src/bridge/state.py

@@ -0,0 +1,73 @@
+"""State file management for OpsBridge."""
+from __future__ import annotations
+
+import os
+from pathlib import Path
+from typing import Optional
+
+from bridge.models import BridgeState
+
+
+def _default_state_dir() -> Path:
+    return Path.home() / ".local" / "state" / "bridge"
+
+
+class StateManager:
+    def __init__(self, state_dir: Optional[Path] = None):
+        self._dir = Path(state_dir) if state_dir else _default_state_dir()
+
+    def _ensure_dir(self) -> None:
+        self._dir.mkdir(parents=True, exist_ok=True)
+
+    def _state_path(self, name: str) -> Path:
+        return self._dir / f"{name}.state"
+
+    def _pid_path(self, name: str) -> Path:
+        return self._dir / f"{name}.pid"
+
+    def read_state(self, name: str) -> BridgeState:
+        path = self._state_path(name)
+        if not path.exists():
+            return BridgeState.STOPPED
+        text = path.read_text().strip()
+        try:
+            return BridgeState(text)
+        except ValueError:
+            return BridgeState.STOPPED
+
+    def write_state(self, name: str, state: BridgeState) -> None:
+        self._ensure_dir()
+        self._state_path(name).write_text(state.value)
+
+    def read_pid(self, name: str) -> Optional[int]:
+        path = self._pid_path(name)
+        if not path.exists():
+            return None
+        try:
+            pid = int(path.read_text().strip())
+        except (ValueError, OSError):
+            return None
+        if _pid_alive(pid):
+            return pid
+        return None
+
+    def write_pid(self, name: str, pid: int) -> None:
+        self._ensure_dir()
+        self._pid_path(name).write_text(str(pid))
+
+    def clear_pid(self, name: str) -> None:
+        path = self._pid_path(name)
+        if path.exists():
+            path.unlink()
+
+    def is_running(self, name: str) -> bool:
+        return self.read_pid(name) is not None
+
+
+def _pid_alive(pid: int) -> bool:
+    """Return True if the process with given PID exists."""
+    try:
+        os.kill(pid, 0)
+        return True
+    except (ProcessLookupError, PermissionError):
+        return False