Fix README links, add missing skills, correct invocation classification

- Fixed 3 broken links in root and common READMEs (pkm-curation,
  forge-interaction, forge-preferences were pointing to wrong buckets)
- Moved project-context-pack from model-invoked to user-invoked
  (matches its disable-model-invocation: true flag)
- Added 8 missing user-invoked and 6 missing model-invoked skills
  to root and common READMEs
- Added all 9 engineering skills to engineering README
  (was missing codebase-design, domain-modeling, resolving-merge-conflicts,
  tdd, grill-with-docs, improve-codebase-architecture, setup-skills,
  to-issues, to-prd, triage)
- Added pkm-curation to pkm README
- Updated personal README to note both skills moved elsewhere
- Added all forge skills to deprecated README
- Added .gitignore for docs/adr/
- Added docs/agents/ reference files
- Added project context cache

common/personal/README.md

@@ -1,9 +1,6 @@
 # Personal Skills
 
-## User-invoked
+_No skills currently live in this bucket._
 
-- [pkm-curation](pkm-curation/SKILL.md) — Curate an Obsidian-style personal knowledge vault.
-
-## Model-invoked
-
-- [forge-preferences](forge-preferences/SKILL.md) — Apply Steve's personal or project-specific forge preferences.
+- `pkm-curation` has been moved to [pkm/pkm-curation](../pkm/pkm-curation/SKILL.md).
+- `forge-preferences` has been moved to [deprecated/forge-preferences](../deprecated/forge-preferences/SKILL.md).