fix(deps): cap nostr-tools at ~2.20.0 (regtest Node 20 / curves v2 ESM-only) (#14)

Caught during regtest dogfood after the previous three commits
landed. With `nostr-tools: ^2.17.2` pnpm resolved to 2.23.5, which
in turn pulls `@noble/curves@2.0.1` — ESM-only. The regtest
Dockerfile runs on Node 20.11.1, where CJS `require()` of pure-ESM
modules is hard-blocked:

  Error [ERR_REQUIRE_ESM]: require() of ES Module
  /app/node_modules/.pnpm/@noble+curves@2.0.1/.../secp256k1.js
  from /app/node_modules/.pnpm/nostr-tools@2.23.5/.../index.js
  not supported.

nostr-tools 2.21.0 was the cutover — that release flipped
`@noble/curves` from `1.2.0` to `2.0.1`. 2.20.0 is the last
nostr-tools 2.x release that's still CJS-friendly via @noble/curves
1.2.0. Capping our pin at `~2.20.0` keeps us within the
"nostr-tools >= 2.17.2" range NDK 3.0.3 asks for in its
peerDependency while sidestepping the ESM/CJS hazard.

This isn't a regression we introduce — it's a CJS-output footgun
unique to the regtest container's Node 20 + tsup-default-CJS
combination. Long-term fix paths (out of scope here):

  * Bump the container's Node base image to >= 22 (where
    `--experimental-require-module` is on by default for `.js`
    files inside `package.json type: "commonjs"`)
  * Switch tsup output to ESM (`tsup --format esm`) — wider
    surface change across the daemon, the client CLI, and the
    Dockerfile entrypoint
  * Accept the cap forever (small downside: 2.21+ patch fixes
    won't reach us until we fix one of the above)

The cap is intentionally tight (`~2.20.0` allows 2.20.x patches,
nothing newer) so a future `pnpm update` doesn't silently jump us
back over the 2.21 edge. Revisit when one of the long-term paths
above lands.

Refs aiolabs/nsecbunkerd#14, regtest dogfood 2026-05-31.

package.json

@@ -57,7 +57,7 @@
     "isomorphic-ws": "^5.0.0",
     "lnbits": "^1.1.5",
     "lnbits-ts": "^0.0.2",
-    "nostr-tools": "^2.17.2",
+    "nostr-tools": "~2.20.0",
     "websocket-polyfill": "^0.0.3",
     "ws": "^8.13.0",
     "yargs": "^17.7.2"