## Summary
Closes [HDX-3784](https://linear.app/clickhouse/issue/HDX-3784/increase-discoverability-of-trace-sources)
- **Context-aware icons for all source kinds**: The data source dropdown now shows icons for every source type — `IconLogs` for logs, `IconConnection` for traces, `IconDeviceLaptop` for sessions, and `IconChartLine` for metrics. Falls back to `IconStack` when no source is selected.
- **Inline source actions**: "Create New Source" and "Edit Sources" actions are now part of the dropdown itself under an "Actions" group with a labeled separator, replacing the separate gear icon menu (`SourceEditMenu`).
- **Dependency update**: Updated `@tabler/icons-react` from v3.5.0 to v3.40.0 to get `IconConnection`.
- **Fix: source management regression when `HDX_LOCAL_DEFAULT_SOURCES` is set**: Before this PR, there were two ways to create/edit sources: (1) options inside the dropdown, which were hidden when `HDX_LOCAL_DEFAULT_SOURCES` is set, and (2) a gear icon button next to the dropdown, which was always visible. This PR removed the gear icon and kept only the dropdown options, but they were still configured to hide when `HDX_LOCAL_DEFAULT_SOURCES` is set — leaving users with no way to manage sources. Fixed by removing that guard so the dropdown options always appear.
<img width="1236" height="492" alt="image" src="https://github.com/user-attachments/assets/6999626b-685b-4037-a003-b09018cfbadf" />
<img width="426" height="240" alt="Screenshot 2026-03-20 at 17 49 30" src="https://github.com/user-attachments/assets/28aaef44-7574-4c54-b721-b2a3a79b3507" />
## Changes
- `packages/app/src/components/SourceSelect.tsx` -- Dynamic left icon based on selected source kind (all 4 kinds: log, trace, session, metric), `onEdit` prop, grouped action items with icons, `renderOption` for source kind and action item icons. Removed `hasLocalDefaultSources` guard so source management actions are always available.
- `packages/app/src/components/SelectControlled.tsx` -- Added `onEdit` callback support, fixed `selected` check to handle grouped data.
- `packages/app/src/DBSearchPage.tsx` -- Removed `SourceEditMenu` component, added `onEditSources` callback, wired `onEdit` to `SourceSelectControlled`.
- `packages/app/styles/SourceSelectControlled.module.scss` -- Group label separator styling with semantic `--color-border` token.
- `packages/app/package.json` -- Updated `@tabler/icons-react` to `^3.39.0`.
## Test plan
- [ ] Select a log source and verify `IconLogs` appears as the left icon
- [ ] Select a trace source and verify `IconConnection` appears as the left icon
- [ ] Select a session source and verify `IconDeviceLaptop` appears as the left icon
- [ ] Select a metric source and verify `IconChartLine` appears as the left icon
- [ ] Verify each source in the dropdown shows its corresponding kind icon
- [ ] Open the dropdown and verify "Create New Source" and "Edit Sources" appear under the "Actions" group with icons
- [ ] Click "Create New Source" and verify the modal opens
- [ ] Click "Edit Sources" and verify navigation to edit (local mode: modal, cloud mode: /team)
- [ ] Verify the gear icon menu is no longer present next to the select
- [ ] **With `NEXT_PUBLIC_HDX_LOCAL_DEFAULT_SOURCES` set**: verify "Create New Source" and "Edit Sources" still appear in the dropdown and work correctly
