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/72-dintel-doc-secretary/code/CLAUDE.md

@@ -24,7 +24,7 @@ from dintel.document import create_branded_doc, save_doc
 from dintel.notion import DB_TASKS_DASHBOARD, CLIENT_DB_MAP
 ```
 
-- **dintel-shared** path: `../dintel-shared/src/dintel/`
+- **_dintel-shared** path: `../_dintel-shared/src/dintel/`
 - `document.py` — DOCX generation with brand styles
 - `brand.py` — Brand constants, colors, prohibited words
 - `notion.py` — Notion DB IDs, client mappings
@@ -107,9 +107,9 @@ The proposal preparation procedure is documented at:
 
 ### Shared References
 
-- Brand constants: `../../dintel-shared/src/dintel/brand.py`
-- Document generator: `../../dintel-shared/src/dintel/document.py`
-- Notion schema: `../../dintel-shared/references/notion-schema-reference.md`
+- Brand constants: `../../_dintel-shared/src/dintel/brand.py`
+- Document generator: `../../_dintel-shared/src/dintel/document.py`
+- Notion schema: `../../_dintel-shared/references/notion-schema-reference.md`
 
 ## Chain Collaborators