fix: mark unavailable sidebar items as coming soon

[saintix4612]

Fix

Settings, Help, and Search currently link to # although their destinations are not implemented. Render them as native disabled buttons with visible “Coming soon” labels and accessible names, as permitted by issue #22. Entries with real destinations retain their existing link behavior and mobile drawer closing.

Closes #22.

Verification

• npm run type-check: passed.
• npm run lint: passed, 13 existing warnings and no errors.
• npm run build: passed; logs include fetch messages from the unconfigured local backend.
• Production build checked on desktop and at 390 × 844 in ego browser: unavailable items are disabled, cannot receive focus, and do not navigate. On mobile, they leave the drawer open; an existing Dashboard link still closes it.
• Uploaded source matches the locally tested source.

Browser checks were manual; no automated regression suite was added. No dependencies, backend behavior, or authorization rules changed. Prepared with OpenAI Codex assistance.

Fix report and screenshots

FIX-REPORT.md