feat: Add grammar fetch and comparison tooling

- Add fetch_bind_grammar.py for MCP-based grammar file retrieval
- Add compare_bind_versions.py for version differences analysis
- Add process_mcp_result.py for handling base64-encoded MCP output
- Create upstream directory structure with fetching instructions
- Document grammar file locations and structure

bind9-grammar/upstream/README.md

@@ -0,0 +1,54 @@
+# BIND9 Grammar Files - Upstream Source
+
+This directory contains upstream BIND9 grammar files from the official BIND9 mirror for version comparison and validation.
+
+## Files to Fetch
+
+When grammar files are needed, fetch from:
+- **Repository**: https://git.valid.dk/Mirrors/bind9
+- **9.18 Tag**: v9.18.44
+- **9.20 Tag**: v9.20.18
+
+### Required Grammar Files (from doc/misc/)
+
+- options
+- forward.zoneopt
+- hint.zoneopt
+- in-view.zoneopt
+- mirror.zoneopt
+- primary.zoneopt
+- redirect.zoneopt
+- secondary.zoneopt
+- static-stub.zoneopt
+- stub.zoneopt
+- delegation-only.zoneopt
+- rndc.grammar
+- parsegrammar.py
+- checkgrammar.py
+
+## Directory Structure
+
+```
+upstream/
+├── v9.18.44/
+│   ├── grammar/          (Grammar files)
+│   └── metadata.json     (Fetch metadata)
+└── v9.20.18/
+    ├── grammar/          (Grammar files)
+    └── metadata.json     (Fetch metadata)
+```
+
+## Fetching
+
+Option 1: Using git fetch
+```bash
+git clone --depth 1 --branch v9.18.44 https://git.valid.dk/Mirrors/bind9.git /tmp/bind9-9.18
+cp /tmp/bind9-9.18/doc/misc/* bind9-grammar/upstream/v9.18.44/grammar/
+```
+
+Option 2: Using Gitea MCP tools (see scripts/fetch_bind_grammar.py)
+
+## Scripts
+
+- `scripts/fetch_bind_grammar.py` - MCP-based fetcher template
+- `scripts/compare_bind_versions.py` - Grammar comparison tool