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/71-dintel-brand-editor/code/scripts/generate_credential.py

@@ -5,7 +5,7 @@ Brand-compliant DOCX following the D.intelligence Korean Writing Style Guide.
 Tone: ~합니다 존칭 서술체 (service/company intro style)
 
 Agent #71 (dintel-brand-editor) v1.1.0 — D.intelligence Agent Corps
-Shared brand constants: dintel-shared/src/dintel/brand.py
+Shared brand constants: _dintel-shared/src/dintel/brand.py
 """
 
 from docx import Document
@@ -16,7 +16,7 @@ from docx.oxml.ns import qn
 import os
 
 # ── Brand Colors ──────────────────────────────────────
-# See also: dintel-shared/src/dintel/brand.py for canonical values
+# See also: _dintel-shared/src/dintel/brand.py for canonical values
 BRAND_DARK = RGBColor(0x1A, 0x1A, 0x2E)    # Dark navy
 BRAND_PRIMARY = RGBColor(0x2D, 0x2D, 0x44)  # Primary text
 BRAND_ACCENT = RGBColor(0xC8, 0xD6, 0x2C)   # Lime/yellow accent