Availability module

[bart-krakowski]

Parent

#25

What to build

Extract resource availability and advisory conflict detection into a proper module. When registered, the module adds availability-aware validation to the write pipeline and exposes read helpers for rendering blocked time.

Resources carry availability windows (weekday + start/end time), capacity, and before/after buffers. Advisory conflict checking runs over the events currently loaded — it is instant UX feedback, not authoritative. Authoritative validation is the server package's responsibility.

Acceptance criteria

• `AvailabilityModule` plugs into the kernel via the module API (Kernel + module registration API #28)
• `getUnavailableRanges(date)` returns fractional minute ranges (`{ startFraction, endFraction }`) — no pixel values, no `containerHeight` parameter
• `getUnavailabilityDetails()` returns per-resource reasons (outside hours / over capacity / no availability defined)
• Advisory conflict detection fires on `addEvent` and `editEvent`, returning a `conflicts[]` array before the write commits
• Capacity rules (multiple resources, consumption arrays) are correctly checked against overlapping events
• Buffer rules (before/after minutes) are respected in conflict detection
• Removing the `AvailabilityModule` causes availability code to tree-shake out of the bundle

Blocked by

#28