refactor(ast-grep): split cli.ts and constants.ts into focused modules

Extract AST-grep tooling into single-responsibility files:
- cli-binary-path-resolution.ts, sg-cli-path.ts
- environment-check.ts, language-support.ts
- process-output-timeout.ts, sg-compact-json-output.ts

src/tools/ast-grep/environment-check.ts

@@ -0,0 +1,89 @@
+import { existsSync } from "fs"
+
+import { CLI_LANGUAGES, NAPI_LANGUAGES } from "./language-support"
+import { getSgCliPath } from "./sg-cli-path"
+
+export interface EnvironmentCheckResult {
+	cli: {
+		available: boolean
+		path: string
+		error?: string
+	}
+	napi: {
+		available: boolean
+		error?: string
+	}
+}
+
+/**
+ * Check if ast-grep CLI and NAPI are available.
+ * Call this at startup to provide early feedback about missing dependencies.
+ */
+export function checkEnvironment(): EnvironmentCheckResult {
+	const cliPath = getSgCliPath()
+	const result: EnvironmentCheckResult = {
+		cli: {
+			available: false,
+			path: cliPath ?? "not found",
+		},
+		napi: {
+			available: false,
+		},
+	}
+
+	if (cliPath && existsSync(cliPath)) {
+		result.cli.available = true
+	} else if (!cliPath) {
+		result.cli.error = "ast-grep binary not found. Install with: bun add -D @ast-grep/cli"
+	} else {
+		result.cli.error = `Binary not found: ${cliPath}`
+	}
+
+	// Check NAPI availability
+	try {
+		require("@ast-grep/napi")
+		result.napi.available = true
+	} catch (error) {
+		result.napi.available = false
+		result.napi.error = `@ast-grep/napi not installed: ${
+			error instanceof Error ? error.message : String(error)
+		}`
+	}
+
+	return result
+}
+
+/**
+ * Format environment check result as user-friendly message.
+ */
+export function formatEnvironmentCheck(result: EnvironmentCheckResult): string {
+	const lines: string[] = ["ast-grep Environment Status:", ""]
+
+	// CLI status
+	if (result.cli.available) {
+		lines.push(`[OK] CLI: Available (${result.cli.path})`)
+	} else {
+		lines.push("[X] CLI: Not available")
+		if (result.cli.error) {
+			lines.push(`  Error: ${result.cli.error}`)
+		}
+		lines.push("  Install: bun add -D @ast-grep/cli")
+	}
+
+	// NAPI status
+	if (result.napi.available) {
+		lines.push("[OK] NAPI: Available")
+	} else {
+		lines.push("[X] NAPI: Not available")
+		if (result.napi.error) {
+			lines.push(`  Error: ${result.napi.error}`)
+		}
+		lines.push("  Install: bun add -D @ast-grep/napi")
+	}
+
+	lines.push("")
+	lines.push(`CLI supports ${CLI_LANGUAGES.length} languages`)
+	lines.push(`NAPI supports ${NAPI_LANGUAGES.length} languages: ${NAPI_LANGUAGES.join(", ")}`)
+
+	return lines.join("\n")
+}