fix(ingestion): close the PR #152 review findings on REST auth

- main.go's wiring was untested (the test built its own copy of the
  router, so dropping auth in main or re-registering POST /query as
  public stayed green). Routing is now one function, buildMux, which
  main calls and the tests call: it constructs the bearer middleware
  itself, registers public handlers only for patterns on a fixed
  allowlist (a public REST pattern would beat the authenticated
  catch-all by specificity), refuses an empty token, and returns an
  http.Handler so nothing can add a route to the result.
- hyperguild CLI: PassRate sent no token and would 401. Every request
  now goes through brainClient.do, which adds it; the test covers
  Query, Write and PassRate and is named for that.
- ResolveIngestPath returns one refusal for every bad path; the raw
  EvalSymlinks error let a caller probe which server files exist and
  leaked the brain directory.
- PROJECT.md (and derived adapters) and the pass-rate runbook state
  that the REST API needs BRAIN_MCP_TOKEN and is tailnet/in-cluster.

Refs #149

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ingestion/internal/api/ingestpath_root_test.go

@@ -67,3 +67,22 @@ func TestIngestPathDirectoryWalkSkipsSymlinksLeavingTheInbox(t *testing.T) {
 	assert.Contains(t, rec.Body.String(), "skipped")
 	assert.NotContains(t, rec.Body.String(), "SENTINEL-149-OUTSIDE")
 }
+
+// PR #152 review: the raw EvalSymlinks error told an authenticated caller
+// whether any server file existed ("no such file") or was unreadable
+// ("permission denied"), and leaked the brain directory. Every refusal now
+// reads the same.
+func TestResolveIngestPathRefusalsAreIndistinguishable(t *testing.T) {
+	brain := t.TempDir()
+	require.NoError(t, os.MkdirAll(filepath.Join(brain, "raw"), 0o755))
+	var msgs []string
+	for _, p := range []string{"/etc/hostname", "/etc/definitely-not-here-149", "../x", "nope/missing.md", ""} {
+		_, err := api.ResolveIngestPath(brain, p)
+		require.Error(t, err, p)
+		msgs = append(msgs, err.Error())
+		assert.NotContains(t, err.Error(), brain, "refusal for %q leaks the brain dir", p)
+	}
+	for _, m := range msgs[1:] {
+		assert.Equal(t, msgs[0], m)
+	}
+}