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/models/models.go

@@ -0,0 +1,46 @@
+// Package models defines the core data types shared across all packages.
+package models
+
+import "time"
+
+// InstructionStatus represents the lifecycle state of a queue item.
+type InstructionStatus string
+
+const (
+	StatusPending  InstructionStatus = "pending"
+	StatusConsumed InstructionStatus = "consumed"
+)
+
+// Instruction is a single item in the queue.
+type Instruction struct {
+	ID                string            `json:"id"`
+	Content           string            `json:"content"`
+	Status            InstructionStatus `json:"status"`
+	CreatedAt         time.Time         `json:"created_at"`
+	UpdatedAt         time.Time         `json:"updated_at"`
+	ConsumedAt        *time.Time        `json:"consumed_at"`
+	ConsumedByAgentID *string           `json:"consumed_by_agent_id"`
+	Position          int               `json:"position"`
+}
+
+// Settings holds user-configurable runtime parameters.
+type Settings struct {
+	DefaultWaitSeconds     int    `json:"default_wait_seconds"`
+	DefaultEmptyResponse   string `json:"default_empty_response"`
+	AgentStaleAfterSeconds int    `json:"agent_stale_after_seconds"`
+}
+
+// AgentActivity tracks the last time an agent called get_user_request.
+type AgentActivity struct {
+	AgentID        string    `json:"agent_id"`
+	LastSeenAt     time.Time `json:"last_seen_at"`
+	LastFetchAt    time.Time `json:"last_fetch_at"`
+	LastResultType string    `json:"last_result_type"`
+}
+
+// QueueCounts summarises the number of items in each state.
+type QueueCounts struct {
+	PendingCount  int `json:"pending_count"`
+	ConsumedCount int `json:"consumed_count"`
+}
+