feat: Add JSONC support for oh-my-opencode config files (#275)

Uses Microsoft's jsonc-parser package for reliable JSONC parsing:
- oh-my-opencode.jsonc (preferred) or oh-my-opencode.json
- Supports line comments (//), block comments (/* */), and trailing commas
- Better error reporting with line/column positions

Core changes:
- Added jsonc-parser dependency (Microsoft's VS Code parser)
- Shared JSONC utilities (parseJsonc, parseJsoncSafe, readJsoncFile, detectConfigFile)
- Main plugin config loader uses detectConfigFile for .jsonc priority
- CLI config manager supports JSONC parsing

Comprehensive test suite with 18 tests for JSONC parsing.

Fixes #265

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: sisyphus-dev-ai <sisyphus-dev-ai@users.noreply.github.com>

src/shared/jsonc-parser.ts

@@ -0,0 +1,66 @@
+import { existsSync, readFileSync } from "node:fs"
+import { parse, ParseError, printParseErrorCode } from "jsonc-parser"
+
+export interface JsoncParseResult<T> {
+  data: T | null
+  errors: Array<{ message: string; offset: number; length: number }>
+}
+
+export function parseJsonc<T = unknown>(content: string): T {
+  const errors: ParseError[] = []
+  const result = parse(content, errors, {
+    allowTrailingComma: true,
+    disallowComments: false,
+  }) as T
+
+  if (errors.length > 0) {
+    const errorMessages = errors
+      .map((e) => `${printParseErrorCode(e.error)} at offset ${e.offset}`)
+      .join(", ")
+    throw new SyntaxError(`JSONC parse error: ${errorMessages}`)
+  }
+
+  return result
+}
+
+export function parseJsoncSafe<T = unknown>(content: string): JsoncParseResult<T> {
+  const errors: ParseError[] = []
+  const data = parse(content, errors, {
+    allowTrailingComma: true,
+    disallowComments: false,
+  }) as T | null
+
+  return {
+    data: errors.length > 0 ? null : data,
+    errors: errors.map((e) => ({
+      message: printParseErrorCode(e.error),
+      offset: e.offset,
+      length: e.length,
+    })),
+  }
+}
+
+export function readJsoncFile<T = unknown>(filePath: string): T | null {
+  try {
+    const content = readFileSync(filePath, "utf-8")
+    return parseJsonc<T>(content)
+  } catch {
+    return null
+  }
+}
+
+export function detectConfigFile(basePath: string): {
+  format: "json" | "jsonc" | "none"
+  path: string
+} {
+  const jsoncPath = `${basePath}.jsonc`
+  const jsonPath = `${basePath}.json`
+
+  if (existsSync(jsoncPath)) {
+    return { format: "jsonc", path: jsoncPath }
+  }
+  if (existsSync(jsonPath)) {
+    return { format: "json", path: jsonPath }
+  }
+  return { format: "none", path: jsonPath }
+}