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/sg-compact-json-output.ts

@@ -0,0 +1,54 @@
+import { DEFAULT_MAX_MATCHES, DEFAULT_MAX_OUTPUT_BYTES } from "./constants"
+import type { CliMatch, SgResult } from "./types"
+
+export function createSgResultFromStdout(stdout: string): SgResult {
+	if (!stdout.trim()) {
+		return { matches: [], totalMatches: 0, truncated: false }
+	}
+
+	const outputTruncated = stdout.length >= DEFAULT_MAX_OUTPUT_BYTES
+	const outputToProcess = outputTruncated ? stdout.substring(0, DEFAULT_MAX_OUTPUT_BYTES) : stdout
+
+	let matches: CliMatch[] = []
+	try {
+		matches = JSON.parse(outputToProcess) as CliMatch[]
+	} catch {
+		if (outputTruncated) {
+			try {
+				const lastValidIndex = outputToProcess.lastIndexOf("}")
+				if (lastValidIndex > 0) {
+					const bracketIndex = outputToProcess.lastIndexOf("},", lastValidIndex)
+					if (bracketIndex > 0) {
+						const truncatedJson = outputToProcess.substring(0, bracketIndex + 1) + "]"
+						matches = JSON.parse(truncatedJson) as CliMatch[]
+					}
+				}
+			} catch {
+				return {
+					matches: [],
+					totalMatches: 0,
+					truncated: true,
+					truncatedReason: "max_output_bytes",
+					error: "Output too large and could not be parsed",
+				}
+			}
+		} else {
+			return { matches: [], totalMatches: 0, truncated: false }
+		}
+	}
+
+	const totalMatches = matches.length
+	const matchesTruncated = totalMatches > DEFAULT_MAX_MATCHES
+	const finalMatches = matchesTruncated ? matches.slice(0, DEFAULT_MAX_MATCHES) : matches
+
+	return {
+		matches: finalMatches,
+		totalMatches,
+		truncated: outputTruncated || matchesTruncated,
+		truncatedReason: outputTruncated
+			? "max_output_bytes"
+			: matchesTruncated
+				? "max_matches"
+				: undefined,
+	}
+}