Redesign card and panel to match SSH Docker visual style

[Copilot]

The Task Tracker card and panel used a flat, fully-colored card design. This updates both to match the SSH Docker card/panel style from gensyn/ssh_docker.

Card (task-tracker-card.js)

• Replaced full-colored-card with colored header-only + standard card background for content
• Added state badge (semi-transparent pill) in header
• Replaced circular ✓ button with a pill-shaped action button (✓ Mark as done) in the content area
• Switched to full re-render pattern (_render() on every set hass()) — removes the brittle "build once, update cells" approach
• Table text now uses var(--primary-text-color) / var(--secondary-text-color)

Panel (task-tracker-panel.js)

• Each task card gets same header-only coloring via inline style="background:${_stateColor(state)}"
• State badge in header; mark-done moved from header icon to bottom action button row
• Removed obsolete .task-card.done / .task-card.inactive flat-color CSS rules

Shared

• _stateColor(state) added to both components: due→#e74c3c, done→#27ae60, inactive→#3498db
• Card version bumped 1.0.0 → 2.0.0 in const.py to bust HA's resource cache

Original prompt

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This section details on the original issue you should resolve

<issue_title>Card and panel could look better</issue_title>
<issue_description>I really like the layout/design of the card and panel at https://github.com/gensyn/ssh_docker/tree/main/frontend.</issue_description>

<agent_instructions>Please change the Task Tracker card and panel to mimic the SSH Docker card and panel?</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Card and panel could look better #14

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