Widen doc-updater scan window to 3 weeks

[amjithtitus09]

What changed

Widens the daily-doc-updater agentic workflow's scan window from the last 24 hours to the last 3 weeks when looking at ohcnetwork/care for merged PRs/commits to document.

.github/workflows/daily-doc-updater.md (body only — frontmatter untouched):

• Step 1 heading: "Scan Recent Activity (Last 24 Hours)" → "(Last 3 Weeks)".
• Date calc: date -u -d "1 day ago" +%Y-%m-%d → date -u -d "3 weeks ago" +%Y-%m-%d (GNU date on the ubuntu runner supports "3 weeks ago"), still feeding the merged:>=YYYY-MM-DD search filter.
• All prose references to "last 24 hours" / "yesterday" updated to "last 3 weeks": the mission statement, the Step 1 search_pull_requests / list_commits bullets, the PR-description template, and the No recent changes edge case. (Grepped the file for 24 hours / 1 day / yesterday — zero remaining.)
• The ohcnetwork/care targeting from Point doc-updater at ohcnetwork/care for change detection #17 and the pre_activation check throttle are unchanged.

.github/workflows/daily-doc-updater.lock.yml regenerated with gh aw compile (extension pinned to v0.81.6):

• Only body_hash changes; frontmatter_hash, compiler_version (v0.81.6) and engine version (copilot 1.0.65) are unchanged.
• Verified a second gh aw compile is a no-op (idempotent). The untracked .github/aw/actions-lock.json and agentics-maintenance.yml are not committed.

⚠️ Heads-up: daily schedule + 3-week lookback = repeated re-scans

This workflow runs on a daily schedule (schedule: daily in the frontmatter), but now looks back 3 weeks. That means every day it re-scans the same ~3 weeks of merged ohcnetwork/care PRs — including ones it already documented on previous runs. There is no dedupe against already-documented changes, so the agent may open duplicate [docs] PRs for work that's already been covered.

The existing MAX_OPEN_PRS=8 pre_activation throttle (gh pr list --repo "$GITHUB_REPOSITORY" ... in:title "[docs]") only caps the number of concurrently-open [docs] PRs — it does not deduplicate content, so you can still get repeated/overlapping doc PRs churning day to day until the cap is hit.

Suggested follow-ups (out of scope for this PR — flagging for the maintainer):

• Add dedupe logic (e.g. have the agent check for existing open/recent [docs] PRs or already-documented PR numbers before creating a new one), and/or
• Move to a less frequent schedule (e.g. weekly) so the lookback window and cadence are better aligned.