Commit the Firestore security rules that were never in source control

SAAS_PLAN.md's review found the actual finding underneath "no multi-tenancy":
drb-frontend reads Firestore directly from the browser (every hook in lib/
does onSnapshot(collection(db, ...))), so drb-c2-core/app/internal/auth.py
is never in that read path at all. Whatever rules were protecting calls,
incidents, and nodes had been hand-set in the Firebase console -
unversioned, unreviewed, and invisible to anyone reading this repo.

Added infra/firestore/firestore.rules: deny-by-default, with every
tenant-scoped collection (nodes, systems, calls, incidents, alert_events,
alert_rules) gated on resource.data.org_id == request.auth.token.org_id, an
org_id claim that doesn't exist yet - the next commits add it. All client
writes stay denied; c2-core's admin SDK bypasses rules and remains the sole
writer, which was already the architecture. Secret-bearing collections
(node_keys, the new enrollment_tokens) are denied to clients outright rather
than org-scoped, since nothing should ever hand a raw credential to the
browser. trips/trip_events keep their current "signed-in users can read"
shape rather than being pulled into org scoping - that feature isn't
tenant-scoped in this pass (see B7), just hidden from non-founding-org users
in the UI.

Added infra/firestore/firestore.indexes.json for the composite indexes the
org_id-scoped queries will need once the frontend hooks add the equality
filter alongside their existing orderBy/range/array-contains clauses -
without these, those queries fail at runtime with a FAILED_PRECONDITION
"index required" error rather than at review time.

Also extended internal/firestore.py's collection_where() with optional
order_by/limit_to/start_after params (SAAS_PLAN.md item 1, a stated
prerequisite for B2: scoped queries need to stay ordered and bounded, and
the existing helper could only do unordered full-collection scans).
array_contains needed no new code - it was already a pass-through op string
to FieldFilter.

None of this is live yet. Deploying rules/indexes is a manual step
(firebase deploy --only firestore:rules,firestore:indexes --project
<project-id>, from infra/firestore/) - nothing in CI does this. Until it
runs, the console-configured rules are still what's actually enforced, and
these rules reference an org_id claim no token carries yet. Deploy this
alongside (not before) the org_id-stamping commits that follow, or every
read breaks for the current single-org deployment.

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

drb-c2-core/app/internal/firestore.py

@@ -68,16 +68,41 @@ async def collection_list(collection: str, **filters) -> list[dict]:
 async def collection_where(
     collection: str,
     conditions: list[tuple[str, str, Any]],
+    order_by: Optional[list[tuple[str, str]]] = None,
+    limit_to: Optional[int] = None,
+    start_after: Optional[dict] = None,
 ) -> list[dict]:
     """
     Query a collection with arbitrary where-clauses.
     conditions: list of (field, op, value) — e.g. [("ended_at", ">=", cutoff_dt)]
-    Supports any Firestore operator: "==", "!=", "<", "<=", ">", ">=".
+    Supports any Firestore operator, including "array_contains" — it's just
+    forwarded straight to FieldFilter, so a condition like
+    ("incident_ids", "array_contains", incident_id) already worked before this
+    function grew explicit order_by/limit/cursor params below.
+
+    order_by: list of (field, direction) — direction is "ASCENDING" or
+      "DESCENDING" (Firestore's own constants; passed straight through as
+      strings so this module doesn't need a google.cloud.firestore_v1.Query
+      import). Applied in list order, so multi-field sorts work.
+    limit_to: cap the number of documents returned.
+    start_after: cursor — a dict of the same field values as the *last*
+      document from a previous page's order_by fields (Firestore's
+      `Query.start_after()` takes a field-value mapping, not a document
+      snapshot, when you're not holding one).
+
+    Added for org_id-scoped queries that also need to be ordered/paginated —
+    unscoped equality-only lookups can keep using collection_list().
     """
     def _query():
         ref = db.collection(collection)
         for field, op, value in conditions:
             ref = ref.where(filter=FieldFilter(field, op, value))
+        for field, direction in (order_by or []):
+            ref = ref.order_by(field, direction=direction)
+        if start_after is not None:
+            ref = ref.start_after(start_after)
+        if limit_to is not None:
+            ref = ref.limit(limit_to)
         return [doc.to_dict() for doc in ref.stream()]
 
     return await asyncio.to_thread(_query)