feat: parse_lua_surface accepts both explicit and sugar-form (S2 follow-up)

Per user-greenlight option (b): function M.foo(...) syntax sugar is now
recognized in addition to M.foo = function(...) explicit-assignment.

Eliminates 7 false-positive stale_docs warnings on every existing lib
README (e.g. lib-core.input). Sugar-form is dominant in Sporel-lib code
(113 occurrences across lib-core/) - sticking to explicit-only would
have required cascade-migrating all init.lua files. This approach is
pragmatic: lint tolerant of idiomatic Lua, no source-rewriting needed.

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

init.lua

@@ -3,18 +3,35 @@
 local M = {}
 
 -- Extracts public/private surface from Lua source code.
--- Convention: `M.<name> = function(...)` is public; `M._<name> = ...` is private.
+-- Convention: M.<name> public; M._<name> private.
+-- Supports both explicit assignment (`M.foo = function`) and syntax sugar
+-- (`function M.foo`) — Lua treats them semantically identical.
 -- Returns: { public = ["foo","bar",...], private = ["_baz",...] }
 function M.parse_lua_surface(source_string)
     local public  = {}
     local private = {}
-    for name in string.gmatch(source_string, "M%.([_%w]+)%s*=%s*function") do
+    local seen    = {}
+
+    local function classify(name)
+        if seen[name] then return end
+        seen[name] = true
         if string.sub(name, 1, 1) == "_" then
             table.insert(private, name)
         else
             table.insert(public, name)
         end
     end
+
+    -- Form 1: M.foo = function(...)
+    for name in string.gmatch(source_string, "M%.([_%w]+)%s*=%s*function") do
+        classify(name)
+    end
+
+    -- Form 2: function M.foo(...)
+    for name in string.gmatch(source_string, "function%s+M%.([_%w]+)") do
+        classify(name)
+    end
+
     return { public = public, private = private }
 end