Add Opera cache cleaner extension baseline

opera-cache-cleaner-extension/AGENTS.md

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+# Agent Instructions
+
+## Project
+
+Opera Cache Cleaner is an Opera-compatible Chromium extension that clears only the browser cache for a selected time range and can optionally schedule repeated cache cleanup.
+
+## Repository Rules
+
+- Preserve the plain Manifest V3 extension structure. Do not add a framework unless the user explicitly asks for it.
+- Keep runtime code in `background.js` and `popup/`.
+- Keep permissions minimal. The extension currently uses only `browsingData`, `storage`, and `alarms`.
+- Do not add host permissions, network calls, cookie/history access, or broad browser permissions without documenting the reason.
+- Do not create a release unless the user explicitly asks for one.
+- Keep `.codex/project.md` aligned when commands, artifact paths, or release rules change.
+
+## Commands
+
+Use these commands from the repository root:
+
+```bash
+node --check background.js
+node --check popup/popup.js
+mkdir -p dist && zip -r dist/opera-cache-cleaner-extension.zip manifest.json background.js popup icons -x "*.DS_Store"
+```
+
+There is no package manager, dependency install, lint, or dependency audit command for the current project.
+
+## Artifacts
+
+Expected release artifact:
+
+```text
+dist/opera-cache-cleaner-extension.zip
+```
+
+## Finish Checklist
+
+- `git diff --check` passes when the project is inside a Git repository.
+- `node --check background.js` passes.
+- `node --check popup/popup.js` passes.
+- Release documentation is updated when release behavior changes.