Add new styles for home and landing pages

- Created home.css with comprehensive styles for the home page layout, including typography, buttons, and responsive design adjustments.
- Created landing.css to style the landing page, focusing on typography, layout, and responsive behavior for various screen sizes.

docs/API.md

@@ -52,6 +52,7 @@ Count habit, with daily resets by default:
 ```json
 {
   "name": "Hydration",
+  "color": "#426582",
   "method": "count",
   "target": 8,
   "unit": "glasses",
@@ -86,6 +87,8 @@ A habit has exactly one method. Incompatible settings are rejected. A switch to
 
 Names are trimmed, nonempty and at most 200 characters. Count targets are integers from 1 to 10,000. Logged counts are nonnegative integers up to 1,000,000,000 and can exceed the target; completion intensity caps at full. Units default to `steps` and are at most 80 characters. A task habit supports at most 100 task definitions.
 
+Creation and habit PATCH accept an optional six-digit hex `color` for all three methods. It is saved atomically as the habit calendar's `mainColor`, separately from dated requirements. Omitting it preserves the default on creation or the current color on edit. Habit PATCH preserves all other calendar settings; the calendar-settings endpoint remains available for replacing the complete settings object.
+
 ## Schedules
 
 Omitted habit or task schedules default to daily. Both rules must match for a task occurrence to exist.