Add Opera cache cleaner extension baseline

opera-cache-cleaner-extension/docs/security-review.md

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+# Security Review
+
+## Scope
+
+Project:
+
+```text
+Opera Cache Cleaner
+```
+
+Reviewed version or commit:
+
+```text
+1.0.0 local workspace
+```
+
+## Code Patterns Checked
+
+- [x] No `eval`.
+- [x] No dynamic `Function` constructor.
+- [x] No unsafe HTML injection found in the reviewed code.
+- [x] No shell execution.
+- [x] No external network calls.
+- [x] No secrets committed in the current source files.
+- [x] No unsafe file writes. Browser data changes are limited to cache removal.
+
+## Dependency Review
+
+Command:
+
+```bash
+No dependency audit command exists because the project has no package manifest or external dependencies.
+```
+
+Result:
+
+```text
+Not applicable.
+```
+
+## Runtime Review
+
+- [x] Manifest uses least-privilege permissions for the current feature set.
+- [x] No host permissions are declared.
+- [x] Local storage is used only for selected range, timer settings, and last run timestamp.
+- [x] Cache clearing uses `chrome.browsingData.remove({ since }, { cache: true })`.
+
+## Release Notes
+
+Known residual risks:
+
+```text
+No automated browser-extension integration tests exist. Perform an unpacked-extension smoke test in Opera before release.
+```