Session memory extraction + tiered context loading improvements

- /review-all-gdds, /architecture-review, /story-done: auto-append Session
  Extract block to active.md after report write (verdict, flags, next action)
- /review-all-gdds, /architecture-review, /create-epics-stories, /content-audit:
  L0 summary scan phase before full document load (reduces token cost)
- GDD template: added Summary section + Cross-References table + Last Verified field
- ADR template: added Summary section + Last Verified field

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/skills/story-done/SKILL.md

@@ -269,6 +269,20 @@ If yes, edit the story file:
    - Update the top-level `updated` field
    - This is a silent update — no extra approval needed (already approved in step above)
 
+### Session State Update
+
+After updating the story file, silently append to
+`production/session-state/active.md`:
+
+    ## Session Extract — /story-done [date]
+    - Verdict: [COMPLETE / COMPLETE WITH NOTES / BLOCKED]
+    - Story: [story file path] — [story title]
+    - Tech debt logged: [N items, or "None"]
+    - Next recommended: [next ready story title and path, or "None identified"]
+
+If `active.md` does not exist, create it with this block as the initial content.
+Confirm in conversation: "Session state updated."
+
 ---
 
 ## Phase 8: Surface the Next Story