fix(mcp,typecheck): prune the imports the contract migration orphaned, and make the root typecheck catch them

The stdio migration left ~40 imports and shape constants unreferenced once every
tool started resolving its schemas through getToolContract. @loopover/mcp's own
tsconfig sets noUnusedLocals, so its package build failed on all of them -- twice
-- while 'npm run typecheck' and the full unit suite stayed green locally.

That gap is the real bug, and it is fixed here rather than worked around: the
root 'typecheck' script now runs the root tsconfig AND each package whose config
is stricter than it (@loopover/contract, @loopover/mcp, @loopover/miner). A bare
'npm run typecheck' now covers the same surface CI's build steps do, so this
class of failure cannot pass locally and fail in CI again.

Also defaults preflight_local_diff's baseRef at the call site. It is optional in
the shared contract input -- the remote server has no checkout to read -- so the
local diff collector needs the 'HEAD' default the stdio-only shape used to bake
into the schema.

Author: JSONbored

package-lock.json

@@ -97,7 +97,9 @@
     "changelog:check:mcp": "node --experimental-strip-types scripts/check-changelog.ts --mcp",
     "mcp:release-due": "tsx scripts/check-mcp-release-due.ts --json",
     "mcp:release-candidate": "tsx scripts/check-mcp-release-candidate.ts",
-    "typecheck": "tsc --noEmit",
+    "typecheck": "npm run typecheck:root && npm run typecheck:packages",
+    "typecheck:root": "tsc --noEmit",
+    "typecheck:packages": "tsc -p packages/loopover-contract/tsconfig.json --noEmit && tsc -p packages/loopover-mcp/tsconfig.json --noEmit && tsc -p packages/loopover-miner/tsconfig.json --noEmit",
     "check-node-version": "node --experimental-strip-types scripts/check-node-version.ts",
     "pretest": "npm run check-node-version",
     "test": "vitest run",