feat(test-management): add listTestPlans and getTestPlan tools

[manoj-k04]

Summary

• Adds listTestPlans and getTestPlan MCP tools, exposing BrowserStack Test Plans as first-class objects (previously agents fell back to test runs when given a TP-* identifier).
• getTestPlan chains GET /test-plans/{id} + GET /test-plans/{id}/test-runs and returns a unified payload: metadata, linked runs, total test-case count across runs, and a derived run-state summary — suitable for auto-generating test documentation / QA status reports.
• listTestPlans covers discovery when the TP-* identifier is not known, mirroring the existing listTestRuns pattern.

Customer context

This is driven by a customer use case (Danske / Himanshu's Slack thread): they want to auto-generate Confluence test documentation from a Test Plan ID via MCP. Current behavior either returns test runs or nothing. This PR covers 4 of the 5 fields they asked for:

Customer ask	Covered
Metadata (id, name, status, description)	✅ getTestPlan
Linked Epics / Requirements	❌ Not in the public Test Plans API — tracked as a follow-up
Linked Test Runs	✅ getTestPlan
Scope (# of test cases)	✅ getTestPlan — total_test_cases derived from linked runs
Status summary	✅ getTestPlan — status_summary + test_runs_count

Test plan

• npm test — 127 passing (4 new tests: success + error for each tool)
• npx tsc --noEmit — clean
• npm run lint — clean
• npm run build — produces dist/tools/testmanagement-utils/{list-testplans,get-testplan}.js
• Stdio smoke test: tools/list via dist/index.js advertises both listTestPlans and getTestPlan
• Live smoke test against a real BrowserStack TM project with a real TP-* (pending reviewer)

🤖 Generated with Claude Code