feat: agents read cross-tool instruction files at session start

AGENTS.md, CLAUDE.md, copilot-instructions.md, and .cursorrules may
contain project knowledge added by other tools or people. Agents now
read these files at session start and merge new knowledge into
.memory/knowledge.md as the canonical source.

.config/opencode/commands/bootstrap-memory.md

@@ -28,6 +28,10 @@ Create (if missing):
 Run `git ls-files` to understand the project layout, then read `README.md` and
 the highest-signal files for architecture and conventions.
 
+Also check for existing cross-tool instruction files (`AGENTS.md`, `CLAUDE.md`,
+`.github/copilot-instructions.md`, `.cursorrules`) — they may contain project
+knowledge from other tools or team members that should be incorporated.
+
 Identify:
 - What the project does (primary capabilities)
 - Core modules/subsystems and responsibilities