docs: add shared Canadaverse agent hygiene

AGENTS.md

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+# Canadaverse project agent rules
+
+These instructions apply to the whole repository. More specific instructions in a nested `AGENTS.md` take precedence for that subtree.
+
+## Start clean
+
+- Read `README.md`, release notes, workflow files, and relevant docs before editing.
+- Run `git status --short --branch` and inspect recent commits. Existing changes belong to their author; do not overwrite, reset, reformat, or bundle them into your work.
+- Use a `codex/<task>` branch or an isolated worktree. Rebase or fast-forward from the current default branch before delivery; never force-push shared branches.
+- Keep the diff scoped. Avoid speculative refactors, dependency churn, generated noise, and unrelated formatting.
+
+## Keep the repository clean
+
+- Do not commit build directories, caches, virtual environments, `node_modules`, logs, temporary captures, device backups, or downloaded release artifacts unless the repository explicitly tracks a generated deliverable.
+- On the shared Windows workstation, keep builds, caches, worktrees, and temporary files on `F:`. Do not consume `C:` for firmware/toolchain output.
+- Use existing scripts and pinned tool versions. Do not introduce a dependency when the standard library or an existing dependency covers the task.
+- Run `git diff --check` and leave the worktree clean after committing.
+
+## Protect secrets and user data
+
+- Never commit credentials, `.env` files, Wi-Fi passwords, API keys, MQTT credentials, Cloudflare tokens, MeshCore private keys, device identity dumps, live databases, packet captures, or user messages.
+- Use synthetic or redacted fixtures and screenshots. Treat radio identities, locations, and private channels as user data.
+- Do not weaken authentication, public/private API boundaries, or safe defaults merely to simplify testing.
+
+## Firmware and hardware
+
+- Resolve the exact board, USB identity, build environment, partition/offset, and release artifact before flashing. Never probe or flash unrelated serial devices.
+- Preserve bootloaders, SoftDevices, identities, contacts, channels, preferences, and NVS/SPIFFS data unless an explicitly labeled recovery operation requires otherwise.
+- Keep board-specific changes guarded. Regression-build an existing target when shared code changes.
+- Hardware claims require evidence from the exact build and device. A green compile is not physical qualification.
+
+## Web and services
+
+- Preserve accessibility, keyboard operation, reduced-motion behavior, mobile layouts, privacy boundaries, and existing public routes.
+- Before deployment, identify the exact host, service/container, mounted paths, current hashes, and rollback boundary. Never restart or modify unrelated Pi services.
+- Verify desktop plus 390 px and 320 px layouts, public links/assets, console output, service health, and restart count after deployment.
+
+## Builds, releases, and completion
+
+- Prefer focused checks first, then the repository's existing CI. Do not invent a second build or release system.
+- A release must come from a clean exact commit, with passing required checks, artifact and manifest hashes, accurate filenames/docs, and clear install versus recovery guidance.
+- Do not create, move, or replace tags/releases unless the user explicitly requested a release.
+- Report what was actually verified. Mark untested hardware, external delivery, or physical behavior as unverified rather than inferring success.