Add FreeDMR1 agent guidance

AGENTS.md

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+# FreeDMR1 Agent Notes
+
+This repository is the FreeDMR 1.x production-maintenance tree.
+
+## Role
+
+- Live HBLink-derived FreeDMR peer server codebase.
+- Current operational behaviour and regression baseline.
+- Keep stable for deployed systems and release candidates.
+
+## Rules
+
+- Do not add DAVE/FreeDMR2 scaffold code or architecture artifacts here unless explicitly requested.
+- Keep changes surgical and compatible with the existing 1.x architecture.
+- Update tests, changelog and user/operator documentation for behaviour changes.
+- Preserve packet bytes unless production code intentionally rewrites them.
+- Treat `bridge_master.py`, `hblink.py`, `bridge.py`, packet routing, dial-a-TG, loop control, source quench and data forwarding as protocol-sensitive.
+- Do not rewrite large parts of the packet path for style alone.
+
+## Related Repos
+
+- `../DAVE/` is the clean successor architecture track.
+- `../FreeDMR-IPSC-Concentrator/` and `../FreeDMR-YSF-Concentrator/` are access/concentrator projects.
+- `../Docker-FreeDMR-IPSC/` is the legacy IPSC container chain.