Run gap analysis bi-weekly (1st and 15th) instead of monthly

[jpr5]

What

Changes the gap-analysis automation cadence from monthly to bi-weekly — it now runs on the 1st and 15th of each month at 04:00 UTC (after the nightly reindex), instead of only the 1st.

• Cron: 0 4 1 * * → 0 4 1,15 * *

Analysis window unchanged

The 30-day analysis lookback window is unchanged (GAP_ANALYSIS_DAYS=30). Only the run cadence changed. Each run still analyzes the trailing 30 days; consecutive runs now overlap, which is intentional — the state-artifact new-gap diffing already de-dupes previously-alerted gaps.

Label / wording edits (cadence-accuracy only)

Removed now-inaccurate "Monthly" cadence wording from user-facing labels:

• .github/workflows/monthly-gap-analysis.yml
  • Workflow name: Monthly Gap Analysis → Gap Analysis (cadence-agnostic)
  • Schedule comment rewritten to describe 1st & 15th, preserving the "after the nightly reindex" rationale
  • Header + upload-step comments: "~30 days" / "next monthly run" cadence references corrected to "~2 weeks" / "next run"
• scripts/gap-analysis/monthly-gap-analysis.ts
  • Console banner === Pathfinder Monthly Gap Analysis === → === Pathfinder Gap Analysis ===
  • File doc-header "Monthly (30-day lookback)" → "Bi-weekly (30-day lookback)"
  • Internal comment "a monthly false-positive Slack storm" → "a recurring false-positive Slack storm"
• scripts/gap-analysis/README.md
  • Title # Monthly Gap Analysis → # Gap Analysis
  • "on the 1st of each month" → "on the 1st and 15th of each month"

Not touched

• Filenames unchanged (monthly-gap-analysis.yml, monthly-gap-analysis.ts, test file) — external tooling references them; the workflow's own gh run list --workflow=monthly-gap-analysis.yml and the weekly-search-report's cross-references still resolve.
• The weekly search-query report is untouched.
• Unrelated uses of "monthly" and the 30-day window are untouched.

Verification

• git grep "0 4 1 \* \*" → zero hits (old cron gone)
• New cron 0 4 1,15 * * is a valid 5-field expression (04:00 UTC on day-of-month 1 and 15)
• actionlint clean, prettier --check clean on touched files, tsc build clean, full test suite green (3554 passed / 1 skipped)