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

infra/matrix/docker-compose.dev.yml

@@ -0,0 +1,60 @@
+# ============================================================================
+# docker-compose.dev.yml — Synapse DEV homeserver for RFC-001 P1 (presence)
+# ============================================================================
+#
+#   *** DEV-ONLY. LOCAL SANDBOX. Do NOT point this at, or run alongside, any
+#       live/production homeserver. ***
+#
+# Single-instance Synapse (RFC-002 Mode B, federation OFF) + an optional
+# Element web client for the human view (A4). Brought up by ./dev-up.sh, which
+# renders config into ./.data (gitignored) first.
+#
+# Isolated by design: dedicated project name + network + high host ports so it
+# never collides with other stacks on the box (A5).
+#
+#   Host ports:  ${MATRIX_HTTP_PORT:-18008}  -> Synapse 8008 (plain HTTP)
+#                ${MATRIX_TLS_PORT:-18448}   -> Synapse 8448 (self-signed TLS)
+#                ${ELEMENT_PORT:-18080}      -> Element web (profile: element)
+# ----------------------------------------------------------------------------
+name: matrix-p1-dev
+
+services:
+  synapse:
+    image: matrixdotorg/synapse:latest
+    container_name: matrix-p1-synapse
+    restart: 'no'
+    # Run against the rendered config in /data (dev-up.sh puts it there).
+    environment:
+      SYNAPSE_CONFIG_DIR: /data
+      SYNAPSE_CONFIG_PATH: /data/homeserver.yaml
+    volumes:
+      - ./.data:/data
+    ports:
+      - '127.0.0.1:${MATRIX_HTTP_PORT:-18008}:8008'
+      - '127.0.0.1:${MATRIX_TLS_PORT:-18448}:8448'
+    networks:
+      - matrix-p1-net
+    healthcheck:
+      test: ['CMD-SHELL', 'curl -fsS http://localhost:8008/health || exit 1']
+      interval: 3s
+      timeout: 5s
+      retries: 40
+      start_period: 5s
+
+  # Optional human view (A4). `docker compose --profile element up -d element`.
+  element:
+    image: vectorim/element-web:latest
+    container_name: matrix-p1-element
+    restart: 'no'
+    profiles: [element]
+    volumes:
+      - ./.data/element-config.json:/app/config.json:ro
+    ports:
+      - '127.0.0.1:${ELEMENT_PORT:-18080}:80'
+    networks:
+      - matrix-p1-net
+
+networks:
+  matrix-p1-net:
+    name: matrix-p1-net
+    driver: bridge