fix(cli): bump the nirium dependency past the deprecated ^0.15.0 pin

[Eras256]

Closes #102.

The bug

packages/cli/package.json pinned "nirium": "^0.15.0". Under semver on
a 0.x package that range is >=0.15.0 <0.16.0 — it excludes 0.16.0.
Confirmed: semver.satisfies('0.16.0', '^0.15.0') is false. A fresh
npm install nirium-cli has been resolving nirium@0.15.0 since 0.16.0
shipped, silently missing everything in that release (the pre-sign
policy hook, the spend-cap error message, the initMpp() fix).

The fix

Bumped to ^0.16.0. package-lock.json regenerated for real — rm -rf node_modules && npm install from the changed package.json, not a
hand-edit — and confirmed it resolves nirium@0.16.0.

Noted, not touched here

npm install warns that @stellar/mpp@0.7.1 (nirium's own transitive
dependency) peer-wants @stellar/stellar-sdk@^15.1.0, while this
package pins ^14.5.0 directly. I checked whether this bump introduces
that warning — it doesn't: reverted the version locally and reinstalled,
same warning fires identically against 0.15.0. The CLI only uses its
own @stellar/stellar-sdk to call Keypair.fromSecret() for printing a
public key; the secret crosses into nirium's initX402() as a plain
string, never a Keypair instance, so the two installed copies don't
share an object across the boundary as far as I traced it. Real warning,
worth its own look, just not one this PR causes or fixes.

Verified

• semver.satisfies('0.16.0', '^0.15.0') → false (the bug, confirmed
  programmatically before touching anything).
• Clean npm install resolves nirium@0.16.0 in the lockfile, both
  immediately after editing package.json and again after a full
  rm -rf node_modules && npm install.
• nirium pay --help and node --check bin/nirium.js both still run
  clean against the new install.

🤖 Generated with Claude Code

[Eras256]

No check ran here: both workflows filter by path (sdk-test.yml on packages/sdk/**, test-verify-audit-cid.yml on actions/verify-audit-cid/**), so nothing under packages/cli/ triggers CI. Adding that coverage is #103.

Tested by hand instead, on current main (c7c8283, which already has #108 and #110) with this branch merged on top:

• merge: clean
• npm ci then npm ls nirium: nirium@0.16.0
• npm test in packages/cli: 11 pass, 0 fail
• node bin/nirium.js --version: 1.1.4

Merging on that basis.

Co-Authored-By: Claude Opus 5.5 noreply@anthropic.com