Expand recent Linear API MCP tool coverage

[itz4blitz]

Summary

This PR expands the Linear MCP server to cover recent stable Linear API surfaces while upgrading the SDK baseline to @linear/sdk ^86.0.0.

Included changes:

• Adds customer and customer-need tools, handlers, validation, service normalization, and docs.
• Adds initiative update lifecycle support with diff metadata.
• Expands comment support beyond issues to projects, initiatives, updates, document content, posts, and replies.
• Adds project lookup by ID, issue relation deletion, broader project create/update fields, project channel metadata, team visibility/parent output, and release date fields.
• Adds top-level MCP argument validation so unsupported tool arguments fail before handler dispatch.
• Updates README.md and TOOLS.md for the expanded public MCP surface.

Tests

This was developed with focused Jest coverage for the new MCP surface and service behavior.

Validation run:

npm test
npm run build
git diff --check

Results:

• Jest: 25 suites passed, 172 tests passed.
• MCP smoke test: passed for 185 tools, 6 resources, and 4 prompts.
• TypeScript build: passed.
• Diff whitespace check: clean.

Notes

Customer write tools are implemented and unit-tested, but live customer creation depends on the Linear workspace having Customers enabled.

A few recent Linear surfaces are intentionally left out because they do not currently have a stable SDK-backed, stateless MCP fit in this implementation: Linear Diffs review operations, AgentSkill management, team resource section/pin writes, and realtime subscriptions.