docs: reference guides for stamdata, audit log, feature flags + document-feature skill

Three how-it-works/how-to-extend reference docs (docs/reference/), each with a
coupling section, indexed in docs/README.md. New document-feature skill so docs
ship in the same diff as the code.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.claude/skills/document-feature/SKILL.md

@@ -0,0 +1,54 @@
+---
+name: document-feature
+description: Ship docs in the same diff as the code — add a doc for a new feature, update the existing doc when a feature changes. Use whenever you add a feature or adjust one that is already documented.
+---
+
+# Document feature (docs travel with the code)
+
+A feature change is not done until its docs match. **Same diff, not a follow-up.**
+Undocumented behavior is a bug; stale docs are worse than none.
+
+## New feature → add the right kind of doc
+
+The repo splits docs by kind (`docs/README.md`). Pick one — don't write all three:
+
+- **Reference doc** — `docs/reference/<name>.md`. A stable "how it works + how to extend
+  without coupling" page. Default for a feature others will build on or wire into.
+  Shape: follow `docs/reference/roles-and-access.md` (H1 title, intro that links the
+  governing ADR/WP, task-oriented `##` sections, `## See also` footer of backticked paths).
+- **ADR** — `docs/reference/architecture/NNNN-<slug>.md`. Only when you're recording a
+  *decision/pattern* (a tradeoff, a "we chose X over Y"). One format, no drift:
+  `# ADR-NNNN — Title`, then `Status: Accepted · Date: YYYY-MM-DD`, then
+  Problem / Options / Decision / Consequences.
+- **WP** — `docs/project/backlog/WP-NN-<slug>.md`. Tracked work; use the template at the
+  bottom of `docs/project/backlog/README.md`.
+
+Then **add the index row**: `docs/README.md` table for a reference doc/ADR,
+`docs/project/backlog/README.md` for a WP. A doc with no index row is invisible.
+
+## Adjusted feature → update what already describes it
+
+Before you call the change done: `grep -ril <feature-name> docs/` and update every hit —
+the reference doc's "how to extend" and coupling notes, the ADR's Consequences, the WP's
+Outcome/Acceptance. If the change makes a doc claim false, fix the claim in this diff.
+
+## Coupling is the interesting part
+
+For any feature others consume, the doc's most valuable section is **how to extend it and
+where the coupling lives** — which shared seams it touches (`ADMIN_LINKS`, the
+`role.interceptor` ROLE_AWARE list, `Capability`), and any hand-wired pattern a second
+consumer would repeat. Name the coupling; recommend the abstraction only when a real
+second case lands (don't refactor speculatively).
+
+## Worked examples
+
+- `docs/reference/stamdata.md`, `docs/reference/audit-log.md`,
+  `docs/reference/feature-flags.md` — the three admin-feature reference docs.
+- `docs/reference/architecture/0004-stamdata-as-code.md` — the decision behind stamdata.
+
+## Verify
+
+```bash
+grep -ril <feature-name> docs/     # every place that mentions it is current
+grep -q "<new-doc-path>" docs/README.md   # (or backlog/README.md) — index row exists
+```