feat: Add version management, session tracking, and commit linking

Phase 1: Version Management
- Migration 006: Add git_tag, git_sha columns to versions
- New tools: version_add, version_list, version_show, version_update,
  version_release, version_assign_task
- Links versions to git tags for release tracking

Phase 2: Session/Task Activity Tracking
- Migration 007: Create task_activity table
- Track task changes per session (created, updated, status_change, closed)
- Session ID from env/cache file (usage-stats format)
- New tool: session_tasks to query tasks by session

Phase 3: Commit-Task Linking
- Migration 008: Create task_commits junction table
- New tools: task_commit_add, task_commit_remove, task_commits_list,
  task_link_commits (batch parsing)
- Stores SHA references only (Gitea MCP owns full data)
- Commits shown in task_show output

17 new MCP tools total. All migrations applied to docker-host postgres.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

migrations/007_task_activity.sql

@@ -0,0 +1,16 @@
+-- Migration 007: Task activity tracking for session integration
+-- Tracks which tasks were touched per session for audit trail
+
+CREATE TABLE IF NOT EXISTS task_activity (
+    id SERIAL PRIMARY KEY,
+    task_id TEXT NOT NULL REFERENCES tasks(id) ON DELETE CASCADE,
+    session_id TEXT NOT NULL,
+    activity_type TEXT NOT NULL CHECK (activity_type IN ('created', 'updated', 'status_change', 'closed')),
+    old_value TEXT,
+    new_value TEXT,
+    created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_task_activity_session ON task_activity(session_id);
+CREATE INDEX IF NOT EXISTS idx_task_activity_task ON task_activity(task_id);
+CREATE INDEX IF NOT EXISTS idx_task_activity_time ON task_activity(created_at DESC);