release: bump version 0.12.0 -> 0.13.0

feat(landing): schema descriptions + refreshed shared page (v3)

- describe.json producer emits an optional per-schema `doc` (the schema
  comment); JSON Schema updated to allow it; golden regenerated.
- Vendored landing.html v3: Markdown tables, table/view/function/schema
  descriptions on expand, two-tier green/blue Cupola CTA, INSTALL line
  before LOAD, footer copyright line.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: rustyconover

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "vgi-python"
-version = "0.12.0"
+version = "0.13.0"
 description = "Vector Gateway Interface - Connect DuckDB to external programs via Apache Arrow"
 readme = "README.md"
 keywords = [

tests/landing/describe.expected.json

@@ -14,6 +14,7 @@
       "name": "example",
       "schemas": [
         {
+          "doc": "Example tables backed by functions",
           "functions": [],
           "name": "data",
           "tables": [
@@ -248,6 +249,7 @@
           ]
         },
         {
+          "doc": "Example functions for testing VGI",
           "functions": [
             {
               "args": [