fix(scripts,mcp): restore actionlint's .ts specifier and drop a dead shape #9565 added

Two rebase follow-ups after #9565 and #9574 landed.

1. scripts/actionlint.ts gets its `.ts` extension back. This PR had removed it to satisfy
   check-import-specifiers, which broke the script outright -- it runs under
   `node --experimental-strip-types`, whose ESM resolver does no extension resolution, so
   the process dies at startup with ERR_MODULE_NOT_FOUND. #9565 independently reached the
   same conclusion and added TYPE_STRIPPED_ENTRYPOINTS to the checker for exactly this
   file, so the extension is now permitted where it is required. Verified by running
   `npm run actionlint`, which fails before this change and passes after.

   #9565's version of the checker is taken wholesale over this PR's: it solves the same
   two problems (that entrypoint set, plus allowlisting check-dead-source-files-script.test.ts
   for its string fixtures), and re-litigating a file main just rewrote buys nothing.

2. src/mcp/server.ts's `loginRepoPullShape` is removed -- dead on arrival in #9565, and
   the first thing the newly-enabled noUnusedLocals caught on main. Which is the point of
   this PR: dead code now surfaces at the commit that introduces it rather than at the next
   audit.

The engine bump lands at 3.16.1 (main released 3.16.0 while this was open). It is required
by check-engine-parity: this PR removes two dead TYPE-only imports from
packages/loopover-engine/src/advisory/gate-advisory.ts, and the parity contract holds that
file in lockstep with its host twin src/rules/advisory.ts. There is no matching host edit to
make -- the engine copy is a deliberately slimmed re-implementation (#4881) omitting the
functions that use those types -- so the version bump is the sanctioned way to record a
one-sided change. No behaviour change: type-only imports are erased at compile time.
packages/loopover-miner/expected-engine.version moves with it, as its own check requires.

Author: JSONbored

scripts/actionlint.ts

@@ -2,7 +2,7 @@ import { readFileSync, readdirSync } from "node:fs";
 import { createRequire } from "node:module";
 import { join } from "node:path";
 import { setTimeout as delay } from "node:timers/promises";
-import { resolveActionlintDownloadAttempts } from "./lib/actionlint-download-attempts";
+import { resolveActionlintDownloadAttempts } from "./lib/actionlint-download-attempts.ts";
 import type { ActionlintOptions, ActionlintResult } from "github-actionlint";
 import type { Result } from "@tktco/node-actionlint/build/types.js";
 

src/mcp/server.ts

@@ -761,13 +761,6 @@ export const gatePrecisionOutputSchema = {
 };
 
 
-const loginRepoPullShape = {
-  login: z.string().min(1),
-  owner: z.string().min(1),
-  repo: z.string().min(1),
-  pullNumber: z.number().int().positive(),
-};
-
 
 const predictGateShape = {
   login: z.string().min(1),