feat(comms): P1 presence — minimal Synapse + fleet presence room + mosaic.presence heartbeat + liveness

Implements RFC-001 P1 (the first shippable slice): deterministic Matrix
presence/liveness on a single-instance dev Synapse.

- infra/matrix/: DEV Synapse (RFC-002 Mode B, federation OFF, self-signed TLS,
  enable_registration:false, appservice registration wired). Rendered from
  parameterized templates — zero hardcoded topology. .data is gitignored.
- packages/comms/: minimal MACP presence SDK — set presence, run the
  mosaic.presence heartbeat (seq + interval per RFC-001 §4.5), and a
  deterministic liveness reader (online/away/offline from heartbeat age, NOT
  native-presence-timeout). Liveness core written RED-FIRST. 19 vitest tests.
- tools/matrix-presence-harness/: minimal provisioner (registers >=3 agent
  MXIDs, creates the fleet presence room, joins them — reuses the existing
  @mosaicstack/appservice intent lib) + an E2E validation harness proving
  A2/A3/A4 against a real Synapse.
- eslint.config.mjs: register packages/comms/vitest.config.ts with the
  type-aware project service (same as other packages' vitest configs).

DEV-compose validated only; production deploy is a separate coordinated step
(deploy-holds respected).

Part of the comms-evolution program (RFC-001 P1)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0158NZqN2n2ymKFeJAZ4GUCb

packages/comms/src/index.ts

@@ -0,0 +1,42 @@
+/**
+ * @mosaicstack/comms — MACP presence SDK (RFC-001 P1).
+ *
+ * Minimal, dev-validated slice: set Matrix presence, run the `mosaic.presence`
+ * heartbeat, and compute deterministic fleet liveness. Enrollment, room
+ * taxonomy, token minting and signed-authorship are explicitly out of P1.
+ */
+
+export { classifyLiveness, computeFleetLiveness } from './liveness.js';
+
+export {
+  HeartbeatEmitter,
+  startHeartbeatLoop,
+  type HeartbeatAgentIdentity,
+  type HeartbeatEmitterOptions,
+  type HeartbeatSender,
+  type HeartbeatLoopOptions,
+  type HeartbeatLoopHandle,
+} from './heartbeat.js';
+
+export {
+  MinimalMatrixClient,
+  MatrixError,
+  toMatrixPresence,
+  type MatrixClientConfig,
+} from './matrix-client.js';
+
+export { FleetLivenessReader, type FleetLivenessReaderOptions } from './liveness-reader.js';
+
+export { PresenceAgent, type PresenceAgentOptions } from './presence-agent.js';
+
+export {
+  DEFAULT_LIVENESS_POLICY,
+  MACP_VERSION,
+  type AgentLiveness,
+  type HeartbeatObservation,
+  type LivenessPolicy,
+  type MacpEnvelope,
+  type MatrixPresence,
+  type PresenceHeartbeatContent,
+  type PresenceStatus,
+} from './types.js';