kbsearch: Go implementation with daemon model serving

- New nested module bin/kbsearch with Go implementation of bin/kb/search
- Embedding model (potion-multilingual-128M) served by localhost daemon
  so repeated CLI calls reuse the loaded model
- Bash launcher bin/kb/search builds binary on first run, caches to var/bin/
- Hybrid FTS + vector search (RRF k=60) matching Python kblib behavior
- YAML output via port of yamlout.py (ordered keys, same format)
- JSON output with proper field order
- All flags: --root, --repo, -n, --json, --list-model
- Root go.mod reverted to 1.25.0 (kbsearch is isolated nested module)
- CI passes: go test ./... and go vet ./... unaffected by kbsearch

bin/kbsearch/types.go

@@ -0,0 +1,16 @@
+// Common types and helpers for kbsearch.
+package main
+
+import "os"
+
+func eps() string { return os.Getenv("KBTEST_EPS") }
+
+// Hit is one search result, mirroring the python script's dict shape.
+type Hit struct {
+	ID      string  `json:"id"`
+	Text    string  `json:"text"`
+	Root    string  `json:"root"`
+	Source  string  `json:"-"` // for repo filtering, not in output
+	Score   float64 `json:"score"`
+	Snippet string  `json:"snippet,omitempty"`
+}