Go through TODOs

[taoeffect]

Problem

Various TODOs in #1 need to be fixed when appropriate, e.g.:

      # TODO: BEGIN REMOVEME (okTurtles/chel#150)
      # chel cannot fetch its own SQLite library, so scripts/chel.mjs points it
      # at the system one. Usually already present.
      - name: Make sure the system SQLite library is there
        run: |
          if [ ! -f /usr/lib/x86_64-linux-gnu/libsqlite3.so.0 ]; then
            sudo apt-get update
            sudo apt-get install -y libsqlite3-0
          fi
      # TODO: END REMOVEME (okTurtles/chel#150)

And others mentioned in AGENTS.md:

## Workarounds waiting on an upstream release

Each one is fenced in the source with `TODO: BEGIN REMOVEME (issue)` and
`TODO: END REMOVEME (issue)`, so `grep REMOVEME` finds them all.

- `scripts/chel.mjs` and `.github/workflows/ci.yml`: the published
  `@chelonia/cli` 3.4.0 cannot load SQLite on its own, so chel is run with
  `DENO_SQLITE_PATH` pointing at the system library. Fixed by
  [chel#162](https://github.com/okTurtles/chel/pull/162), tracked as
  [chel#150](https://github.com/okTurtles/chel/issues/150). Until a release
  ships, run chel as `node scripts/chel.mjs <args>`.
- `src/contracts/identity.js`, `src/chelonia/config.js`,
  `scripts/build-contracts.mjs`: the account contract has to be named
  `gi.contracts/identity`, Group Income's name, because chel only accepts a
  contract created without an account to bill it to under that exact name.
  [chel#160](https://github.com/okTurtles/chel/issues/160).
- `src/chelonia/auth.js`, `lookupUsername`: replaced by
  `chelonia/out/nameToContractID` once a `@chelonia/lib` release has
  [libcheloniajs#90](https://github.com/okTurtles/libcheloniajs/issues/90).
- `src/chelonia/auth.js`, signup error message: the publish error carries the
  HTTP status once a release has the fix for
  [libcheloniajs#94](https://github.com/okTurtles/libcheloniajs/issues/94).
- `src/chelonia/auth.js`, `USERNAME_REGEX`: a copy of chel's private
  `NAME_REGEX`. Goes once chel exports the rule.
- `src/chelonia/auth.js`, the key list in `signup`: gets shorter once
  [libcheloniajs#91](https://github.com/okTurtles/libcheloniajs/issues/91)
  lands. Not a removal, so it is a plain TODO.

Solution

Go through them all and apply the relevant fixes.

[akhileshthite]

@taoeffect Yep, most of them will get resolved once we release a new version of chel. Will make a new PR for that.

[akhileshthite]

@taoeffect we can close this, addressed in #7