Lint rule: forbid importing other features' internals

Prevention follow-up to the 2026-07-13 `formatBytes` stage break. The setup for that break was a cross-feature reach-in: `features/instance/databases/**` importing from `features/instance/status/analytics/**` internals. When the status feature refactored its internals (as it's entitled to), the other feature broke.

**Rule to enforce:** code under `src/features//` may not import from `src/features//**` for `Y ≠ X` (same-feature and `src/lib`/`src/components`/`src/hooks`/`src/integrations` imports stay fine). When something is genuinely needed across features, promote it to `src/lib`/`src/components` first (see PR #1494 for the pattern).

**Mechanism (verify what our oxlint version supports):**
- Preferred: oxlint `no-restricted-imports` with per-feature path patterns, if our version supports pattern-based restrictions (`.oxlintrc.json`). The local `oxlint --rules` output was empty in a quick check — needs a look at the docs for the pinned version.
- Fallback: a ~20-line CI script (grep-based) in Verify PR that fails on `@/features/` imports outside their own feature tree — crude but sufficient and dependency-free.

Current known violations to fix or exempt when enabling: none after PR #1494 (DatabaseOverview was the only one; verify with a fresh grep when implementing).

Comment generated by kAIle (Claude Fable 5)