refactor: reorganize skill numbering, remove obsolete skills, rename shared libs

- Rename: 00→80 claude-settings-optimizer, 88→79 dintel-skill-update,
  92→81 mac-optimizer, 93→82 tui-design-template
- Rename: dintel-shared → _dintel-shared (consistent with _ourdigital-shared)
- Remove: 61-gtm-manager, 62-gtm-guardian (obsolete), 99_archive
- Update all dintel-* skill refs (114 occurrences across 31 files)
- Sync README.md, CLAUDE.md, AGENTS.md with new structure

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

custom-skills/75-dintel-marketing-mgr/code/CLAUDE.md

@@ -9,7 +9,7 @@ Manage D.intelligence's marketing content pipeline: Magazine D. articles, newsle
 - **Agent #75** — Marketing Manager
 - **Autonomy**: Draft & Wait — drafts content, waits for Andrew's approval before publishing
 - **Collaborates with**: Agent #71 (Brand Editor) for writing check, Agent #70 (Brand Guardian) for compliance review
-- **Shared constants**: `dintel-shared/src/dintel/brand.py` (colors, terminology, style tokens)
+- **Shared constants**: `_dintel-shared/src/dintel/brand.py` (colors, terminology, style tokens)
 
 ## Universal Guardrails
 
@@ -27,8 +27,8 @@ Manage D.intelligence's marketing content pipeline: Magazine D. articles, newsle
 - **Internal Motto**: Think Forward
 - **Keywords**: Context, Content, Connection
 - **Concept**: SMART Marketing Clinic
-- **Brand Guide**: `../../dintel-shared/references/dintelligence_brand_guide.md`
-- **Shared Constants**: `../../dintel-shared/src/dintel/brand.py`
+- **Brand Guide**: `../../_dintel-shared/references/dintelligence_brand_guide.md`
+- **Shared Constants**: `../../_dintel-shared/src/dintel/brand.py`
 
 ## Training & Education Materials