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/db/db.go

@@ -0,0 +1,77 @@
+// Package db manages the SQLite connection and schema migrations.
+package db
+
+import (
+	"database/sql"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	_ "modernc.org/sqlite" // pure-Go SQLite driver, no CGo required
+)
+
+// schema creates all tables if they do not already exist.
+const schema = `
+CREATE TABLE IF NOT EXISTS instructions (
+    id                   TEXT PRIMARY KEY,
+    content              TEXT NOT NULL,
+    status               TEXT NOT NULL DEFAULT 'pending',
+    created_at           TEXT NOT NULL,
+    updated_at           TEXT NOT NULL,
+    consumed_at          TEXT,
+    consumed_by_agent_id TEXT,
+    position             INTEGER NOT NULL DEFAULT 0
+);
+
+CREATE INDEX IF NOT EXISTS idx_instructions_status   ON instructions(status);
+CREATE INDEX IF NOT EXISTS idx_instructions_position ON instructions(position);
+
+CREATE TABLE IF NOT EXISTS settings (
+    key   TEXT PRIMARY KEY,
+    value TEXT NOT NULL
+);
+
+CREATE TABLE IF NOT EXISTS agent_activity (
+    agent_id         TEXT PRIMARY KEY,
+    last_seen_at     TEXT NOT NULL,
+    last_fetch_at    TEXT NOT NULL,
+    last_result_type TEXT NOT NULL
+);
+`
+
+// defaultSettings seeds initial values; OR IGNORE means existing rows are unchanged.
+const defaultSettings = `
+INSERT OR IGNORE INTO settings (key, value) VALUES ('default_wait_seconds',     '10');
+INSERT OR IGNORE INTO settings (key, value) VALUES ('default_empty_response',   '');
+INSERT OR IGNORE INTO settings (key, value) VALUES ('agent_stale_after_seconds','30');
+`
+
+// Open opens (creating if necessary) a SQLite database at dbPath, applies the
+// schema, and seeds default settings.
+func Open(dbPath string) (*sql.DB, error) {
+	dir := filepath.Dir(dbPath)
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		return nil, fmt.Errorf("create db directory: %w", err)
+	}
+
+	db, err := sql.Open("sqlite", dbPath+"?_pragma=journal_mode(WAL)&_pragma=foreign_keys(on)&_pragma=busy_timeout(5000)")
+	if err != nil {
+		return nil, fmt.Errorf("open database: %w", err)
+	}
+
+	// Serialise all writes through a single connection to avoid locking.
+	db.SetMaxOpenConns(1)
+
+	if _, err := db.Exec(schema); err != nil {
+		_ = db.Close()
+		return nil, fmt.Errorf("apply schema: %w", err)
+	}
+
+	if _, err := db.Exec(defaultSettings); err != nil {
+		_ = db.Close()
+		return nil, fmt.Errorf("seed settings: %w", err)
+	}
+
+	return db, nil
+}
+