fix: improve config validation error handling

[Zebastjan]

Supersedes #171 - this is a clean version without the unintended batch tool files.

Problem

When OctoFriend encounters configuration errors (e.g., invalid MCP server config or JSON5 syntax errors), it crashes with an unhelpful error message:

TypeError: [object Object] failed the following checks:
[archon]: undefined
at Err.toError (/usr/lib/node_modules/octofriend/node_modules/structural/build/lib/result.js:16:16)
...

Solution

This PR adds comprehensive error handling that:

• Catches and explains JSON5 parsing errors
• Detects invalid MCP server configurations and provides specific guidance
• Exits gracefully with helpful error messages and examples
• Suggests remediation steps (e.g., octofriend init to start fresh)

Changes

• source/config.ts: Added try-catch blocks for JSON5 parsing and schema validation with detailed error messages
• source/cli.tsx: Added graceful error handling in runMain() to exit cleanly on config errors

Test plan

• Tested with invalid MCP server configuration (missing command field)
• Tested with JSON5 syntax errors (missing commas)
• Verified error messages are clear and helpful
• Build passes successfully
• Pre-commit hooks pass

[sdjidjev]

I like having more clear error messaging, especially as we add more configurability!
Just a note about how to we can clean the MCP servers validation logic

[sdjidjev]

i think this'll be a lot cleaner if we just do:

    const mcpServers = raw["mcpServers"];
    if (mcpServers && typeof mcpServers === "object") {
      const invalidServers: string[] = [];
      for (const [name, serverConfig] of Object.entries(mcpServers)) {
        try {
          McpServerConfigSchema.slice(serverConfig);
        } catch {
          invalidServers.push(name);
        }
      }
      if (invalidServers.length > 0) {
        throw new Error(
          `Invalid MCP server configuration in ${filePath}: ${invalidServers.join(", ")}\n\n` +
            `Each MCP server must have:\n` +
            `  - command: string\n` +
            `  - args: string[] (optional)\n` +
            `  - env: object (optional)`,
        );
      }
    }

    throw new Error(
      `Configuration file validation failed: ${filePath}\n\n` +
        `Error: ${errorMessage}\n\n` +
        `You can reset your config by deleting: ${filePath}`,
    );