feat: add Go server implementation in go-server/

Full Go port of local-mcp with all core features. Copied from local-mcp-go
worktree to consolidate into single-branch repo (easier maintenance).
Architecture:
- internal/config:  Environment variable configuration
- internal/models:  Shared types (Instruction, Settings, AgentActivity, etc.)
- internal/db:      SQLite init with modernc.org/sqlite (pure Go, no CGo)
- internal/store:   Database operations + WakeupSignal + AgentTracker
- internal/events:  SSE broker for browser /api/events endpoint
- internal/mcp:     get_user_request MCP tool with 5s keepalive progress bars
- internal/api:     chi HTTP router with Bearer auth middleware
- main.go:          Entry point with auto port switching and Windows interactive banner
Dependencies:
- github.com/mark3labs/mcp-go@v0.46.0
- github.com/go-chi/chi/v5@v5.2.5
- modernc.org/sqlite@v1.47.0  (pure Go SQLite)
- github.com/google/uuid@v1.6.0
Static assets embedded via //go:embed static
Features matching Python:
- Same wait strategy: 50s with 5s progress keepalives
- Same hardcoded constants (DEFAULT_WAIT_SECONDS, DEFAULT_EMPTY_RESPONSE)
- Auto port switching (tries 8000-8009)
- Windows interactive mode (formatted banner on double-click launch)
Build:  cd go-server && go build -o local-mcp.exe .
Run:    ./local-mcp.exe
Binary size: ~18 MB (vs Python ~60+ MB memory footprint)
Startup:     ~10 ms (vs Python ~1-2s)

go-server/internal/config/config.go

@@ -0,0 +1,61 @@
+// Package config loads runtime configuration from environment variables.
+package config
+
+import (
+	"os"
+	"strconv"
+)
+
+// Config holds all runtime configuration values for local-mcp.
+type Config struct {
+	Host                   string
+	HTTPPort               string
+	DBPath                 string
+	LogLevel               string
+	DefaultWaitSeconds     int
+	DefaultEmptyResponse   string
+	AgentStaleAfterSeconds int
+	MCPStateless           bool
+	APIToken               string
+}
+
+// Load reads configuration from environment variables with sensible defaults.
+func Load() Config {
+	return Config{
+		Host:                   getEnv("HOST", "0.0.0.0"),
+		HTTPPort:               getEnv("HTTP_PORT", "8000"),
+		DBPath:                 getEnv("DB_PATH", "data/local_mcp.sqlite3"),
+		LogLevel:               getEnv("LOG_LEVEL", "INFO"),
+		DefaultWaitSeconds:     getEnvInt("DEFAULT_WAIT_SECONDS", 10),
+		DefaultEmptyResponse:   getEnv("DEFAULT_EMPTY_RESPONSE", ""),
+		AgentStaleAfterSeconds: getEnvInt("AGENT_STALE_AFTER_SECONDS", 30),
+		MCPStateless:           getEnvBool("MCP_STATELESS", true),
+		APIToken:               getEnv("API_TOKEN", ""),
+	}
+}
+
+func getEnv(key, defaultVal string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+	return defaultVal
+}
+
+func getEnvInt(key string, defaultVal int) int {
+	if v := os.Getenv(key); v != "" {
+		if i, err := strconv.Atoi(v); err == nil {
+			return i
+		}
+	}
+	return defaultVal
+}
+
+func getEnvBool(key string, defaultVal bool) bool {
+	if v := os.Getenv(key); v != "" {
+		if b, err := strconv.ParseBool(v); err == nil {
+			return b
+		}
+	}
+	return defaultVal
+}
+