fix: Address review — remove stale Matrix references from runtime prompts

Critical fixes:
- vault/vault-agent.sh: Update comment and prompt to use PHASE:escalate
  instead of "send a Matrix message"
- dev/dev-agent.sh: Update escalation instruction from "reply via Matrix"
  to "respond via the forge"
- dev/phase-handler.sh: Update build_phase_protocol_prompt() escalation
  text from "reply via Matrix" to "respond via the forge"

Minor fixes:
- bin/disinto: Remove duplicate comment line in docker-compose header
- README.md: Update vault table row from "via Matrix" to "via vault/forge"
- BOOTSTRAP.md: Remove "Matrix credentials" from TOML description
- lib/AGENTS.md: Remove "callers may follow up via Matrix" from
  formula_phase_callback description

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

bin/disinto

@@ -156,7 +156,6 @@ generate_compose() {
   cat > "$compose_file" <<'COMPOSEEOF'
 # docker-compose.yml — generated by disinto init
 # Brings up Forgejo, Woodpecker, and the agent runtime.
-# Brings up Forgejo, Woodpecker, and the agent runtime.
 
 services:
   forgejo: