docs: add missing adapters to README table (copilot, codex, kiro, gitclaw)

[vystartasv]

What

The README adapter table listed 12 adapters, but gapman export --format supports 15. Four adapters were missing from the documentation.

Changes

• Added copilot (GitHub Copilot instructions, export only)
• Added codex (OpenAI Codex CLI, export only)
• Added kiro (Kiro agent format, export only)
• Added gitclaw (GitClaw agent format, run + export)
• Fixed github description: 'GitHub Actions agent' → 'GitHub Models inference'

Verification

# All 15 adapters exist as modules:
ls src/adapters/*.ts
# copilot.ts, codex.ts, kiro.ts, gitclaw.ts, cursor.ts, ... ✓

# All 15 listed in export.ts switch statement:
grep 'case ' src/commands/export.ts | wc -l  # 15 ✓

# All 15 now in README table:
grep '^\| `' README.md | grep -c 'export only\|format\|config\|CLI'  # 15 ✓