fix(best-practices): restore canonical content, dedupe, sync script, spec exemplar

- best-practices/v1: replace 9 stale symlinks (into planning/v1) with real files
  synced byte-identical from the canonical best-practices project; add INDEX.md,
  scripting.md, mechanical-test-generation.md (canonical had drifted heavily,
  e.g. api-design.md 463->807 lines)
- planning/v1: delete duplicated best-practices/ copy (requires: inheritance
  confirmed via spec/harness.md HC-1/HC-7)
- scripts/sync-best-practices.sh: idempotent re-sync from canonical checkout
- code-methodology/v1: INDEX.md + scripting.md references now resolve; point
  test-writing tasks at mechanical-test-generation.md
- spec-writing/v1: worked spec exemplar (module layout table, Why: lines, exact
  error messages, parametrize pattern table) + CLAUDE.md pointer + mount entry

harnesses/contexts/spec-writing/v1/CLAUDE.md

@@ -20,6 +20,14 @@ Before starting any spec, read these from `/workspace/best-practices/`:
 
 Read at minimum the four "Always" files. Read others based on the task domain.
 
+Before drafting, also read the worked exemplar at
+`/opt/harness/context/spec-writing/spec-exemplar.md`. It shows the full section
+structure (module layout table, numbered requirements with Why: lines and exact
+error messages, a pattern table usable as a parametrize matrix, GIVEN/WHEN/THEN
+scenarios) applied to a small invented subsystem. A spec must let a test-writer
+agent produce imports, assertions, and mocks with no other input — the exemplar is
+the bar for that level of concreteness.
+
 ## Spec Structure
 
 Every spec must follow this structure: