fix: replace ts-node-dev with tsx to unbreak dev scripts

[alchemydc]

Why

The typescript 5.9.3 → 7.0.2 bump (#46) broke every ts-node-dev script:

TypeError: Cannot read properties of undefined (reading 'fileExists')
    at readConfig (ts-node/dist/configuration.js:91:33)
    at findAndReadConfig (ts-node/dist/configuration.js:50:84)
    at registerTsNode (ts-node-dev/lib/compiler.js:174:16)

typescript@7 is the native/Go compiler port. Its npm package exports 2 keys total and ts.sys is undefined:

$ node -e "const ts=require('typescript'); console.log(ts.version, typeof ts.sys, Object.keys(ts).length)"
7.0.2 undefined 2

ts-node@10.9.2 reaches for ts.sys.fileExists at startup, so it dies immediately. This took out dev, discord:debug, discourse:debug, and models:list — everything except build (the tsc CLI) and test (vitest transpiles with esbuild). ts-node-dev is unmaintained, so no upstream fix is coming.

What changed

• ts-node-dev → tsx (esbuild-based, never touches the TS compiler API). --transpile-only is dropped since tsx never type-checks; npm run build remains the type-check gate.
• dev is plain tsx src/main.ts, deliberately not tsx watch. main.ts is a one-shot job that posts to Slack — re-running it on every file save is wrong. The old --respawn was a latent footgun.
• Dropped the now-dangling diff override. It existed only to pin ts-node-dev's vulnerable transitive diff; npm ls diff is empty now. The undici override is untouched.
• Removed a stale untracked pnpm-lock.yaml from a local experiment. package-lock.json is the committed lockfile and what npm ci in daily-digest.yml consumes.
• AGENTS.md command list updated to match.

Net 201 packages removed from the lockfile (tsx's tree is much smaller than ts-node-dev's).

Verification

$ npx tsx --version          → tsx v4.23.9
$ npm run models:list        → live Gemini model list returned
$ npm run discourse:debug    → "Discourse debug completed successfully"
$ npm run build              → clean
$ npm test                   → 108/108 passing

I ran the two read-only debug tools rather than npm run dev, since that fires a real digest.

Reviewer notes

• npm install now warns that esbuild@0.28.1 has an unapproved postinstall script (npm's allow-scripts gate). tsx works regardless in local testing, but CI may need npm approve-scripts esbuild if npm ci refuses it. Worth watching on the first run.
• CI may fail for reasons unrelated to this change; GitHub is having an outage as of opening.

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