feat(perf): implement performance optimizations for session handling

- Introduced a new configuration file `config.yaml` for specifying project context and artifact rules.
- Added `.openspec.yaml` files for tracking changes related to performance improvements.
- Created design documents outlining the context, goals, decisions, and migration plans for optimizing session performance.
- Proposed changes include batching database queries, debouncing event refreshes, purging old events, and implementing loading states for better user experience.
- Added tasks and specifications to ensure proper implementation and validation of the new features.

These enhancements aim to improve the scalability and responsiveness of the application during collaborative sessions.

openspec/changes/perf-data-optimization/specs/query-cache-layer/spec.md

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+## ADDED Requirements
+
+### Requirement: Cached session list queries
+Frequently-called session list queries SHALL be cached using Next.js `unstable_cache` with user-scoped tags, avoiding redundant DB reads on repeated navigations.
+
+#### Scenario: Session list served from cache on repeated navigation
+- **WHEN** a user navigates to the sessions page multiple times within the cache window
+- **THEN** the session list data SHALL be served from cache on subsequent requests
+- **THEN** no additional Prisma query SHALL be executed for cached data
+
+#### Scenario: Cache invalidated after mutation
+- **WHEN** a Server Action creates, updates, or deletes a session
+- **THEN** the corresponding cache tag SHALL be invalidated via `revalidateTag`
+- **THEN** the next request SHALL fetch fresh data from the DB
+
+### Requirement: Weather history bounded query
+The weather service SHALL limit historical data loading to a configurable maximum number of entries (default: 90), ordered by most recent first.
+
+#### Scenario: Weather history respects limit
+- **WHEN** the weather service fetches historical entries
+- **THEN** at most `WEATHER_HISTORY_LIMIT` entries SHALL be returned
+- **THEN** entries SHALL be ordered by `createdAt` DESC (most recent first)
+
+### Requirement: Minimal field selection on list queries
+Service functions returning lists for display purposes SHALL use Prisma `select` with only the fields required for the list UI, not full `include` of related models.
+
+#### Scenario: Sessions list query returns only display fields
+- **WHEN** the sessions list service function is called
+- **THEN** the returned objects SHALL contain only fields needed for card display (id, title, createdAt, item count, share status)
+- **THEN** full related model objects (items array, events array) SHALL NOT be included