feat(mcp): add gittensory_get_repo_onboarding_pack MCP tool

[JSONbored]

There is a stdio prompt gittensory_repo_owner_onboarding_pack (packages/gittensory-mcp/bin/gittensory-mcp.js:1250) that presumes an onboarding-pack payload, and buildRepoOnboardingPackPreviewForRepo exists in src/services/repo-onboarding-pack.ts:30, but the hosted MCP server exposes no tool to actually fetch that pack. Add the missing tool so the prompt has a real data source.

Deliverables

• Register gittensory_get_repo_onboarding_pack in src/mcp/server.ts, inputSchema=ownerRepoShape
• Handler calls buildRepoOnboardingPackPreviewForRepo(env, repoFullName) with the repo-access guard
• zod outputSchema for the onboarding-pack preview shape
• Tests: authorized, unauthorized, and unregistered-repo branches

References

• src/services/repo-onboarding-pack.ts:30
• src/services/repo-onboarding-pack.ts:18
• packages/gittensory-mcp/bin/gittensory-mcp.js:1250

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size: S · held for later release (gittensor:feature once activated)

[linear-code]

JSO-2324