feat: add parse_readme_api (S2 Phase 1)

Extracts H3-headers from README ## API section. Pattern handles
optional namespace-prefix (e.g. 'input.bind' -> 'bind'). Returns
{ documented = [...] } per spec section 4.2.

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

init.lua

@@ -18,4 +18,26 @@ function M.parse_lua_surface(source_string)
     return { public = public, private = private }
 end
 
+-- Extracts documented function-names from README's "## API" section.
+-- Parses H3-Headers like "### `input.bind(action_name, keys)`" → "bind".
+-- Convention: H3 header opens with backtick, function-name follows after optional namespace-dot.
+-- Returns: { documented = ["bind","unbind",...] }
+function M.parse_readme_api(markdown_string)
+    local documented = {}
+    -- Find "## API" section start (allow trailing whitespace/content)
+    local api_start = string.find(markdown_string, "\n## API[%s\n]")
+    if not api_start then
+        return { documented = documented }
+    end
+    -- Find next H2 (terminate API section)
+    local api_end = string.find(markdown_string, "\n## ", api_start + 5)
+    local section = string.sub(markdown_string, api_start, api_end or #markdown_string)
+
+    -- Match H3 headers: "### `[namespace.]name(...)`" — capture name portion
+    for line in string.gmatch(section, "###%s+`[^.`]*%.?([_%w]+)%s*[%(`]") do
+        table.insert(documented, line)
+    end
+    return { documented = documented }
+end
+
 return M