Kill the surviving mutants in process-graph #64

src/bin.ts has no in-process test at all, so its peer-dependency check is uncovered; only the smoke test runs the built bin. These are the most-affected files in process-graph on main's mutation run (https://github.com/ExaDev/process-graph/actions/runs/38170535483), with a few of the lines a surviving or uncovered mutant changes; the shard log and the uploaded HTML report have the full list.

packages/targets/process-graph/src/bin.ts (0 survived, 58 without coverage):

• packages/targets/process-graph/src/bin.ts:12:26 StringLiteral mutant, no coverage, on const manifest = new URL("../package.json", import.meta.url);
• packages/targets/process-graph/src/bin.ts:15:50 BlockStatement mutant, no coverage, on const declaredPeers = (): Map<string, string> => {
• packages/targets/process-graph/src/bin.ts:16:61 StringLiteral mutant, no coverage, on const parsed: unknown = JSON.parse(readFileSync(manifest, "utf8"));
• packages/targets/process-graph/src/bin.ts:18:5 ConditionalExpression mutant, no coverage, on typeof parsed !== "object" ||

packages/targets/process-graph/src/missing-peers.ts (1 survived, 0 without coverage):

• packages/targets/process-graph/src/missing-peers.ts:25:4 StringLiteral mutant, survived, on ["npm", "npm install"],

Kill them by asserting the behaviour, not by loosening or removing any existing assertion. Raise the package's breakThreshold from the new baseline once they are killed. Found while setting the break thresholds in #60.