feat: compact display mode with tap actions

[KadenThomp36]

Closes #20.

Summary

Adds a `display: compact` config option that renders just the title + overall status badge in a smaller card, with optional standard HA tap actions to navigate elsewhere on click.

Use case from the issue: a dashboard overview page that shows a single "All Good" indicator that taps through to the full air quality dashboard.

HA-native approach

Tap actions follow HA's documented pattern for custom cards — dispatch a `hass-action` CustomEvent with `{ config, action: 'tap' | 'hold' | 'double_tap' }`. HA's frontend handles the rest (navigate, more-info, call-service, etc.).

The editor uses the standard `ui_action` selector for each action field, giving users the same picker they see in every other HA card.

Implementation

• New `_renderCompact()` renders a much smaller DOM: just the title + status badge in a clickable card
• `set hass` skips `_loadHistory` in compact mode (no graphs → no fetch needed → faster initial render on overview dashboards)
• `_updateStates` early-returns after the badge update in compact mode
• Hold detection uses a 500ms timer; tap is suppressed when a hold fires
• `getCardSize` returns 1 for compact (one row), full size for full mode

Test plan

• `node test.js` — 216 passed, 0 failed (10 new: `_isCompact` flag, `getCardSize` returns 1, `_fireAction` dispatches `hass-action` only when the action is configured, no-op behavior for missing actions)
• Manual smoke test: add a compact card with `tap_action: { action: navigate, navigation_path: /air-quality }` → confirm the card is clickable and navigates correctly
• Manual smoke test: the status badge updates live when sensor values change
• Visual editor: open the editor for a compact card → confirm the display dropdown shows both options and the tap_action picker works

YAML example

```yaml
type: custom:air-quality-card
name: Air Quality
co2_entity: sensor.air_quality_co2
pm25_entity: sensor.air_quality_pm25
display: compact
tap_action:
action: navigate
navigation_path: /lovelace/air-quality
```

Notes for maintainer

• No `CARD_VERSION` bump — will roll into rc2
• Independent of PR feat: support outdoor-only sensor configurations #26/fix: time-based graph x axis + status label corrections #27/feat: optional min/max per metric (show_min_max) #28/feat: per-metric custom thresholds #29 — no expected conflicts