Add pagination to observation list

[bgorzelic]

Problem

getObservations() currently fetches ALL observations for a user with no limit. As users accumulate observations over multiple fire seasons, this will degrade dashboard load times and increase database costs.

Proposed Implementation

• Add page and pageSize parameters to getObservations()
• Default page size: 20 observations
• Add pagination controls below the observations table (Previous / Page N of M / Next)
• Show total count from getObservationStats() (already exists)
• URL-based pagination: /dashboard?page=2
• Mobile: same pagination controls below card list

Acceptance Criteria

• Dashboard loads only 20 observations per page
• Pagination controls visible at bottom of table
• URL updates with page number (shareable/bookmarkable)
• Page 1 loads by default
• Total observation count still accurate in stats cards
• Works on both desktop table and mobile card views
• Empty state still shows when no observations exist