Add efficiency metrics to analyze_trends() #78

Problem

analyze_trends() compares current vs previous period for events, sessions, errors, and tokens - but doesn't include efficiency metrics that would answer "am I getting better at not burning context?"

Proposed Solution

Add efficiency-related metrics to the trends output:

{
    "avg_compactions_per_session": {"current": 4.2, "previous": 5.4, "change_pct": -22},
    "avg_files_read_multiple_times": {"current": 3.1, "previous": 4.8, "change_pct": -35},
    "avg_session_bytes": {"current": 2.1e6, "previous": 2.8e6, "change_pct": -25}
}

Value

This directly answers "are my workflow improvements working?" - the whole point of /improve-workflow.

Implementation

1. Query get_session_efficiency() for both periods
2. Aggregate metrics (avg compactions, avg bytes, avg files read multiple times)
3. Calculate change percentages
4. Add to existing trends output

Related

• Part of efficiency analytics improvements discussed in session
• Complements Add limit parameter to verbose endpoints (get_tool_sequences, get_compaction_events) #77 (limit parameters)