feat: add agent activity feed functionality

[pikann]

Summary

Adds an "Activity" tab to the agent detail page: a unified, cursor-paginated, filterable feed of every task and doc activity a given agent has performed across the project, styled like a log viewer with infinite scroll.

Backend

• New GET /projects/:projectId/agents/:agentId/activities endpoint (services/api/internal/transport/http/handler/agent_handler.go) resolves the agent's project_members.id via memberRepo.FindMemberByAgent, then lists a keyset-paginated (created_at, id) page combining task_activities and doc_activities, filterable by type (task/doc), created_after/created_before, and free-text search (matches the linked task/doc title or activity content).
• AgentRepository.ListAgentActivities (services/api/internal/repository/postgres/agent_repository.go) implements this with a single UNION ALL CTE over both tables joined to tasks/documents for the display title, mirroring the existing conversations cursor-pagination pattern.
• New domain types/cursor in domain/agent/activity_feed.go and cursor.go; new AgentActivityResponse DTO; new AGENT_ACTIVITY_INVALID_CURSOR error code.
• Migration 000030_add_activity_actor_cursor_indexes.sql adds composite (actor_id, created_at DESC, id DESC) indexes on both activity tables (doc_activities previously had no actor index at all).

Frontend

• New AgentActivityTab / AgentActivityFilters components, modeled on the existing Conversations page's IntersectionObserver-driven infinite scroll and filter popover.
• New agentActivitiesQueryOptions cursor-paginated query in agent-api.ts, keyed separately from the "agents" prefix so realtime invalidation can target every agent's feed without over-invalidating other agent caches.
• Exported and lightly narrowed the existing activityDescription/describeDocActivity renderers so the new tab reuses the same activity copy instead of duplicating it.
• Wired a new "Activity" tab into the agent detail page; wired task.*/doc.* realtime events to invalidate the activity feed.
• Translated into all 9 locales (en, es, fr, ja, ko, pt-BR, ru, vi, zh-CN).

Test plan

• go build ./..., go vet ./..., and go test ./... in services/api — new coverage for the query mapping, service passthrough, and every handler branch (missing member repo, wrong project, member not found, invalid type filter, success).
• golangci-lint run ./... in services/api — clean.
• tsc -b, biome check ., and vitest run in apps/web — all clean (345 tests passing).
• Manually verified against the running dev stack: confirmed the new indexes applied to the live DB, and exercised the live endpoint end-to-end (base fetch, type filter, invalid type → 400, search hit/miss, date filter, malformed cursor → 400).

[pullfrog]

✅ No new issues found.

Reviewed changes

This PR adds the agent activity feed feature end-to-end: a new "Activity" tab on the agent detail page, a backend GET /projects/:projectId/agents/:agentId/activities endpoint, and supporting database indexes. The key changes:

• Frontend UI — agent-activity-tab.tsx (infinite-scrolling feed, row links) and agent-activity-filters.tsx (search, source-type checkboxes, date-range popovers).
• Data layer — new AgentActivity* types, agentActivitiesQueryOptions, and localDateStartISO/localDateExclusiveEndISO date conversion in agent-api.ts.
• Cache invalidation — use-project-realtime.ts targets the agentActivities query-key prefix on task.*/doc.* events.
• Copy reuse — activityDescription and describeDocActivity are exported and narrowed to the fields the new feed actually needs.
• i18n — new agents.detail.activity.* keys added to all eight locale files.
• Backend API — cursor codec, domain/repository/service methods, DTO, handler validation, error mapping, and route wiring.
• Database — migration 000030 replaces the single-column idx_task_activities_actor_id with partial composite indexes (actor_id, created_at DESC, id DESC).

ℹ️ Deployment note

000030 drops the old idx_task_activities_actor_id and creates a partial composite index on each activity table. The CREATE INDEX IF NOT EXISTS statements are idempotent, but on a very large task_activities/doc_activities table index creation can lock while it builds. Plan deploy sequencing accordingly for high-traffic tables.

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[pullfrog]

✅ No new issues found.

Reviewed changes

This run covered the two commits since the last pullfrog review (3cbb6a38). The latest changes harden the activity feed around deleted sources and member/sprint name resolution:

• Deleted-source handling — added a source_deleted boolean to the backend ActivityFeedItem, repository CTE, response DTO, and frontend AgentActivity type. The backend now computes (t|d).deleted_at IS NOT NULL in each UNION branch; the UI renders deleted task/document titles as plain text instead of links.
• Member/sprint name resolution — AgentActivityTab now loads projectMembersQueryOptions and sprintsQueryOptions once per project and passes a memoized {members, sprints} lookup map into the shared activityDescription helper, so task activity copy shows names instead of truncated IDs.
• Frontend tests — added agent-activity-filters.test.tsx (search debounce, type toggle, clear-all) and agent-activity-tab.test.tsx (name resolution, fallback IDs, deleted source).
• Backend tests — added TestActivityFeedItemFromRecord_PreservesSourceDeleted and updated existing mapping assertions to cover the new field.

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