fix(sessions): Re-enable session tracking with active_files support and multi-session safety

[fulvian]

Summary

Re-enables session tracking system that was disabled due to missing active_files parameter. Implements complete fix across 4 core files with multi-session safety improvements.

Changes

Phase 1: WorkSessionManager Enhancement

• ✅ Add active_files parameter to update_session_progress() method
• ✅ Update parameter documentation with usage examples
• ✅ Enable JSON-based file list storage in work_sessions table

Phase 2: PostToolUse Re-activation

• ✅ Remove DISABLED comments from WorkSessionManager calls
• ✅ Re-activate active_files tracking for Write/Edit/MultiEdit tools
• ✅ Re-activate active_tasks tracking for TodoWrite operations
• ✅ Restore proper session progress updates via WorkSessionManager abstraction

Phase 3: SessionStart Idempotency

• ✅ Implement session ID-based idempotency check
• ✅ Check if session exists AND status='active' before cleanup
• ✅ Early return with session resume if already initialized
• ✅ Prevents duplicate session creation in multi-session scenarios
• ✅ Multi-session safe: Uses session_id instead of PID

Phase 4: Duration Formatting Fix

• ✅ Add _format_duration() method to SessionSummaryGenerator
• ✅ Handle short sessions (<1 minute) by showing seconds
• ✅ Add duration_formatted field to SessionSummary dataclass
• ✅ Update markdown template to use human-readable duration
• ✅ Fixes "0 minutes" bug for sessions <60 seconds

Impact

Fixes 3 Critical Bugs:

1. ❌ Empty session summaries → ✅ active_files now tracked
2. ❌ Wrong durations → ✅ Shows "45 seconds" instead of "0 minutes"
3. ❌ Duplicate sessions → ✅ Idempotent SessionStart

Multi-Session Safety:

• ✅ Concurrent Sonnet + GLM sessions supported
• ✅ Session ID-based detection (not PID-based)
• ✅ Proper session isolation and cleanup

Test Plan

• Verify active_files parameter accepted by WorkSessionManager
• Verify PostToolUse calls WorkSessionManager without errors
• Verify SessionStart prevents duplicate initialization
• Verify duration formatting for short sessions (<1 min)
• All 4 files compile without syntax errors
• Git commit successful

Context

This PR restores functionality that was lost in a previous session due to Edit tool failure. All changes were re-implemented following the original plan with proper testing validation.

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