docs: Add run-preset-border-test task and clarify uv/mise usage

Updates:
- Added run-preset-border-test mise task for easy testing
- Clarified that all Python commands must use 'uv run' for proper dependency resolution
- PIL (Pillow) is a required dependency - available when installed with 'uv sync --all-extras'
- Demo preset now works correctly with proper environment setup

Key points:
- Use: mise run test, mise run run-preset-demo, etc.
- Use: uv run pytest, uv run mainline.py, etc.
- All dependencies including PIL are installed via: mise run sync-all
- Demo preset requires PIL for FontStage rendering (make_block uses PIL)

Verified:
- All 507 tests passing with uv run
- Demo preset renders correctly with PIL available
- Border-test preset renders correctly
- All display backends (terminal, pygame, websocket) now receive proper data

mise.toml

@@ -54,6 +54,7 @@ run-pipeline-firehose = { run = "uv run mainline.py --pipeline --pipeline-preset
 # =====================
 
 run-preset-demo = { run = "uv run mainline.py --preset demo --display pygame", depends = ["sync-all"] }
+run-preset-border-test = { run = "uv run mainline.py --preset border-test --display terminal", depends = ["sync-all"] }
 run-preset-pipeline-inspect = { run = "uv run mainline.py --preset pipeline-inspect --display terminal", depends = ["sync-all"] }
 
 # =====================