Enhance session reporting and table rendering; add time-range selection in skill metadata

[mouxinqq]

Motivation

• Improve session-level diagnostics by recording request time ranges and prefill URL counts to make reports more actionable.
• Make the interactive skill more explicit about time-range analysis and AskUserQuestion options so clients reliably surface the --start/--end mode.
• Improve Markdown table rendering to produce aligned, readable tables for wide columns in generated reports.

Description

• Update skill metadata (.claude/skills/stat-cache-hitrate/SKILL.md) to add --start/--end time-range mode, require discrete AskUserQuestion options for analysis modes, and clarify output and field names in the session detail description.
• Extend session record generation in session_analysis.py to include first_ts, last_ts, and prefill_url_count for each session row returned by compute_session_details.
• Refactor table rendering in stat_cache_hitrate.py by replacing the simple Markdown header/row construction with a width-aware renderer that pads columns and supports right alignment via align_right.
• Add helpers _seq_label, _extract_seq_num, and _summarize_id_type_ranges to produce compact id-type range summaries and consistent sequence IDs for sessions shown in reports.
• Enhance session report generation in stat_cache_hitrate.py to: compute and display overall analysis time range, summarize contiguous id-type ranges, include purl_cnt and avg-hit columns in compact and full tables, replace some column names for clarity, and include per-session time ranges in the switch details section.

Testing

• Performed a local smoke test by running python3 .claude/skills/stat-cache-hitrate/scripts/stat_cache_hitrate.py sample.log --tail 100 and verified the script completed and produced the skill_output/stat-cache-hitrate/ report files without exceptions.
• No new unit tests were added in this change set.

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Codex Task