test: add validators module and comprehensive test harness

[jesustorres-code]

Summary

• Extracts all argument-validation logic from index.ts into src/validators.ts (parseGitHubRepo, requireNonEmpty, toolError) — replaces 9 inline validation blocks across 8 tool handlers
• Adds test/validators.test.mjs using Node's built-in node:test (zero new dependencies) with 19 test cases
• Wires npm test into ci.yml so the suite gates every PR

Test coverage

parseGitHubRepo (13 cases):

• owner/name — plain shorthand
• https:// and http:// full GitHub URLs
• .git suffix stripping
• .git + trailing slash
• Query string stripping (?tab=issues)
• Fragment stripping (#readme)
• Trailing slash without .git
• Empty string → "repo is required"
• null / undefined → "repo is required"
• No-slash string → "Could not parse repo"
• Whitespace-only → "repo is required"

requireNonEmpty (6 cases):

• Valid string → null (no error)
• Empty string, whitespace-only, null, undefined → isError: true
• Field name appears verbatim in error message

Why this is more complete than PR #24

PR #24 extracts only parseGitHubRepo and applies it to one handler. This PR:

• adds a second generic validator (requireNonEmpty) used across 8 handlers
• replaces all inline validation in index.ts (not just one case), eliminating the duplication
• covers 19 test cases vs 5

Closes #16

[eliottreich]

Thanks for this, genuinely useful work. We've put a funded $10 TaskBounty bounty on the underlying issue: https://www.task-bounty.com/task/taskbounty-mcp-server-16-add-a-test-harness-and-ru-q8mnpc . To claim it, register at https://www.task-bounty.com/, then submit your fix through the platform (REST API, MCP server, or the patch-upload endpoint). It runs against the repo's own tests in an isolated sandbox, and on a verified pass you're paid through escrow in USDC, ETH, BTC, or bank. We keep payment on-platform so it stays verified and auditable for everyone. First verified submission wins it.