feat: add search_code tool wrapping the cs code-search engine

Add a dedicated, permission-gated search_code tool that wraps boyter/cs
(code spelunker) — a fast, relevance-ranked, structure-aware code search
engine — giving agents a better default than grep/find for exploratory
'where is X / how does Y work' searches (ranked results, snippets, ~5x
smaller payloads).

- packages/core/src/tools/search-code.ts: createSearchCodeTool factory;
  -f json invocation, workdir path containment, graceful missing-binary
  handling (DISPATCH_CS_BIN override), readable per-file formatted output.
- Wire-up: export from core; register in agent-manager (both child-whitelist
  and parent perm paths) behind new perm_search_code; add to summon catalog
  + tools enum; frontend ToolPermissions + settings.
- Docker: build a patched, statically-linked cs (pinned v3.1.0 commit) in a
  golang builder stage and bundle at /usr/local/bin/cs.
- docker/cs/luau-declarations.patch: additive Luau declaration table so
  --only-declarations / definition ranking works for Roblox .luau files
  (upstream has Lua but not Luau). Applied during the Docker build.
- Tests: new search-code.test.ts (stubbed JSON formatting + live-cs
  integration, skipped when cs absent); agent-manager/routes mocks +
  perm-gating assertions; loader pass-through.

All tests (596), biome, and tsc (core/api/frontend) pass. cs-builder Docker
stage verified to build and produce a working patched binary.

1 files changed, 32 insertions, 0 deletions

diff --git a/docker/cs/luau-declarations.patch b/docker/cs/luau-declarations.patch
new file mode 100644
index 0000000..794ecac
--- /dev/null
+++ b/docker/cs/luau-declarations.patch
@@ -0,0 +1,32 @@
+Add a Luau declaration-pattern table to the cs structural ranker.
+
+Upstream cs (v3.1.0) ships a "Lua" entry in languageDeclarationPatterns but no
+"Luau" entry, even though its bundled scc database recognises ".luau" files as a
+distinct "Luau" language. Without a matching declaration table, every match in a
+.luau file is classified as a plain "usage": --only-declarations returns nothing
+and the structural ranker gives definitions no boost. This is the dominant file
+type in Roblox codebases, so we add a Luau entry that mirrors Lua's function
+prefixes and additionally covers Luau's `type` / `export type` declarations.
+
+This is a purely additive change (one new map entry); it does not alter any
+existing language's behaviour and passes cs's own pkg/ranker test suite. Applied
+during the Docker build via `git apply` against the pinned v3.1.0 checkout
+(see Dockerfile / Dockerfile.dev). Candidate for upstreaming to boyter/cs.
+
+diff --git a/pkg/ranker/declarations.go b/pkg/ranker/declarations.go
+index 42cd934..36f9f68 100644
+--- a/pkg/ranker/declarations.go
++++ b/pkg/ranker/declarations.go
+@@ -187,6 +187,12 @@ var languageDeclarationPatterns = map[string][]DeclarationPattern{
+ 		{Prefix: []byte("function ")},
+ 		{Prefix: []byte("local function ")},
+ 	},
++	"Luau": {
++		{Prefix: []byte("function ")},
++		{Prefix: []byte("local function ")},
++		{Prefix: []byte("type ")},
++		{Prefix: []byte("export type ")},
++	},
+ 	"Scala": {
+ 		{Prefix: []byte("def ")},
+ 		{Prefix: []byte("val ")},