Reconcile session-report rule in CLAUDE.md docs

[RikepilB]

Problem

Two doc rules still point at the now-removed docs/session-reports/:

• .claude/CLAUDE.md "Session progress reporting"
• docs/CLAUDE.md "Session Report Rule"

They're inconsistent with the new append-only docs/handoff/ tree.

Fix

• Update both to reference the handoff tree (docs/handoff/<date>-<name>/HANDOFF.md + father update), OR explicitly keep session-reports as a separate committed milestone-summary stream — pick one and make both docs agree.
• Verify no other doc references the dead path.

Acceptance

• Both CLAUDE.md files reference the same, current system
• No lingering docs/session-reports/ references that contradict the tree
• Change committed via PR

Notes

Context in docs/handoff/_meta/LATER-TASKS.md ("Session-report rule reconciliation").