fix: Remove Matrix integration — notifications move to forge + OpenClaw (#732)

Remove all Matrix/Dendrite infrastructure:
- Delete lib/matrix_listener.sh (long-poll daemon), lib/matrix_listener.service
  (systemd unit), lib/hooks/on-stop-matrix.sh (response streaming hook)
- Remove matrix_send() and matrix_send_ctx() from lib/env.sh
- Remove MATRIX_HOMESERVER auto-detection, MATRIX_THREAD_MAP from lib/env.sh
- Remove [matrix] section parsing from lib/load-project.sh
- Remove Matrix hook installation from lib/agent-session.sh
- Remove notify/notify_ctx helpers and Matrix thread tracking from
  dev/dev-agent.sh and action/action-agent.sh
- Remove all matrix_send calls from dev-poll.sh, phase-handler.sh,
  action-poll.sh, vault-poll.sh, vault-fire.sh, vault-reject.sh,
  review-poll.sh, review-pr.sh, supervisor-poll.sh, formula-session.sh
- Remove Matrix listener startup from docker/agents/entrypoint.sh
- Remove append_dendrite_compose() and setup_matrix() from bin/disinto
- Remove --matrix flag from disinto init
- Clean Matrix references from .env.example, projects/*.toml.example,
  formulas/*.toml, AGENTS.md, BOOTSTRAP.md, README.md, RESOURCES.md,
  PHASE-PROTOCOL.md, and all agent AGENTS.md/PROMPT.md files

Status visibility now via Codeberg PR/issue activity. Human interaction
via vault items through forge. Proactive alerts via OpenClaw heartbeats.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

projects/disinto.toml.example

@@ -16,12 +16,6 @@ stale_minutes      = 60
 [services]
 containers = []
 
-[matrix]
-room_id      = "!your_room_id:matrix.example.org"
-bot_user     = "@disinto-factory:matrix.example.org"
-token_env    = "DISINTO_MATRIX_TOKEN"
-mention_user = "@johba:matrix.allf.in"  # Matrix user to @mention on escalations
-
 [monitoring]
 check_prs            = true
 check_dev_agent      = true

projects/harb.toml.example

@@ -16,12 +16,6 @@ stale_minutes      = 60
 [services]
 containers = ["ponder"]
 
-[matrix]
-room_id      = "!your_room_id:matrix.example.org"
-bot_user     = "@harb-factory:matrix.example.org"
-token_env    = "MATRIX_TOKEN"
-mention_user = "@johba:matrix.allf.in"  # Matrix user to @mention on escalations
-
 [monitoring]
 check_prs            = true
 check_dev_agent      = true