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>

dev/dev-agent.sh

@@ -574,7 +574,7 @@ phase handler. You do not need to merge or close anything — stop and wait.
 \`\`\`bash
 printf 'PHASE:escalate\nReason: %s\n' \"describe what you need\" > \"${PHASE_FILE}\"
 \`\`\`
-Then STOP and wait. A human will reply via Matrix and the response will be injected.
+Then STOP and wait. A human will review and respond via the forge.
 
 **If refusing (too large, unmet dep, already done):**
 \`\`\`bash