Waypoint graph UI shows "(no screenshot)" for classifier-labeled example captures

## Summary

Waypoints captured with a device classifier render as "(no screenshot)" in the waypoint graph UI until their example files are hand-renamed, because the UI's example loader only resolves the bare `.example.json` sibling and ignores classifier-labeled example files.

## Details

`trailblaze waypoint capture-example` writes classifier-labeled example pairs when the source log records a device classifier — e.g. `.example.android-phone.json` plus its screenshot (see `WaypointCaptureExampleCommand.kt`). It does **not** write a bare `.example.json` in that case.

The example loader used by the waypoint graph UI (`/waypoints/graph`) and the Compose waypoints tab only resolves the bare sibling:

- `trailblaze-host/src/main/java/xyz/block/trailblaze/ui/tabs/waypoints/WaypointsTabComposable.kt` — `tryLoadFilesystemExample` builds `File(waypointFile.parentFile, "$basename.example.json")` (~line 454).
- The trailmap-side loader has the same limitation with `exampleJsonPath = "$basename.example.json"` (~line 605).

As a result, a freshly captured classifier-labeled waypoint has no matching example file from the UI's perspective and renders with no screenshot. The current workaround is to manually rename the classifier-labeled files to the bare form.

## Expected

`WaypointValidateCommand.kt` already understands the full example **set** — the bare `.example.json` plus any `.example..json` siblings (see `resolveSiblingExamples`, ~lines 204–221). The UI loader should mirror that resolution: prefer the bare example, and fall back to a classifier-labeled example (deterministically, e.g. first sorted classifier) when no bare file exists.

## Suggested fix

- Update the example resolution in `WaypointsTabComposable.kt` (both the filesystem loader at ~line 454 and the trailmap loader at ~line 605) to fall back to `.example..json` when the bare file is absent, choosing deterministically.
- Add a test alongside the existing loader tests in `trailblaze-host/src/test/java/xyz/block/trailblaze/ui/tabs/waypoints/`.

Start in trailblaze-host/src/main/java/xyz/block/trailblaze/ui/tabs/waypoints/WaypointsTabComposable.kt, where the filesystem and trailmap loaders resolve example files, and compare their behavior with resolveSiblingExamples in WaypointValidateCommand.kt. Add loader tests alongside the existing tests in trailblaze-host/src/test/java/xyz/block/trailblaze/ui/tabs/waypoints/. Done means classifier-labeled examples load when the bare example is absent, while the bare example remains preferred and fallback selection is deterministic.

Written by the indexing model from the issue text.