fix(memory): remove loading overlay layer

[mattrossman]

• Draw the no-data state from a render-only loading component instead of keeping a separate Pebble loading overlay layer.
• Establish the component pattern under src/c/components while keeping forecast_layer responsible for composition/state decisions.
• mise build passes; latest Aplite RAM footprint is 17,088 B vs 17,312 B before (+224 B free heap).

[github-actions]

✅ Preview dev build available.

Download forecaswatch2-dev-pbw-pr-137.zip

Memory usage

Platform	Resources	RAM footprint	Free heap
Diorite	4,591 bytes / 256.0KB	17,324 bytes / 64.0KB	48,212 bytes
Basalt	4,703 bytes / 256.0KB	17,532 bytes / 64.0KB	48,004 bytes
Aplite	4,365 bytes / 128.0KB	17,088 bytes / 24.0KB	7,488 bytes

Parsed 3 platforms from the build log.

Artifacts are attached to the workflow run/job and require GitHub access to this repository.
Run: #119