Start cleanly when bench is the project itself

Three layout defects broke ./start.sh in the self-hosted repo, one of
which (missing local/state/) broke every fresh vendored install too:

- install.py resolved the project as TM.parent, a hardcoded vendored-
  layout assumption. It now asks git for the toplevel from the manager's
  directory (same resolution as config._repo_root), falling back to the
  parent when git is unavailable — vendored installs still find the host
  repo, self-hosted bench finds itself instead of its parent.

- adapters/claude/wire hardcoded ".task-manager/" into the emit hook
  command and plansDirectory. Both are now derived from the manager's
  path relative to the project root, so vendored installs keep the
  .task-manager/ prefix and self-hosted bench gets prefix-free paths.
  _is_ours also recognises the emit.py suffix, so settings wired with
  the old literal path count as stale and are repaired idempotently.

- board.py and state.py created the sessions/agent dirs without
  parents=True; local/state/ is gitignored and ships empty, so a virgin
  checkout died with FileNotFoundError before serving. Boot now creates
  the whole chain, wiring or no wiring.

tests/test_self_hosting.py (stdlib unittest) covers both layouts' wiring,
stale-path repair, idempotent re-runs, refusal without .claude/, root
resolution with and without git, and an integration boot of board.py
from a scratch checkout with no local/state/.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

install.py

@@ -19,11 +19,31 @@ import sys
 from pathlib import Path
 
 TM = Path(__file__).resolve().parent
-PROJECT = TM.parent
 LOCAL = TM / "manager" / "local"
 CORE = TM / "manager" / "core"
 
 
+def _project_root() -> Path:
+    """The host project's root: the git toplevel seen from the manager's
+    directory (same resolution as config._repo_root). Vendored installs
+    drop .task-manager/.git at clone time, so this finds the host repo;
+    when the manager IS the repo (self-hosted), it finds that repo itself.
+    No git → fall back to the vendored-layout assumption, the parent."""
+    try:
+        out = subprocess.check_output(
+            ["git", "-C", str(TM), "rev-parse", "--show-toplevel"],
+            text=True, stderr=subprocess.DEVNULL,
+        ).strip()
+        if out:
+            return Path(out)
+    except (subprocess.CalledProcessError, OSError):
+        pass
+    return TM.parent
+
+
+PROJECT = _project_root()
+
+
 def adapter_name() -> str:
     if os.environ.get("BOARD_AGENT_ADAPTER"):
         return os.environ["BOARD_AGENT_ADAPTER"]