Stub bundled SKILL.md; read canonical methodology from MCP resource

The bundled skill file was a frozen 542-line copy that only updated on
plugin re-release. Replace it with a thin pointer to the server-side
resource `skill://methodology`, so skill-content changes propagate
without requiring users to reinstall the plugin.

- skills/oci-deal-accelerator/SKILL.md: reduced to ~40-line stub that
  directs Codex to read skill://methodology first, with a minimal
  tool table and fallback behavior if the MCP is unreachable
- .codex-plugin/plugin.json: bump to 0.2.0 (breaking change in what
  the plugin ships; Codex treats new versions as new cache entries)
- .gitignore: ignore Codex CLI's local .codex state file

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.codex-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "oci-deal-accelerator",
-  "version": "0.1.0",
+  "version": "0.2.0",
   "description": "Oracle Cloud Infrastructure deal-acceleration toolkit: proposals, BOMs, cost estimates, diagrams, WA reviews, and reference-architecture search via a remote MCP server.",
   "author": {
     "name": "Diego Cabrera",