fix(backend): correct off-by-one in isValidStellarAddress regex

[Jah-yee]

Summary

Fixes the off-by-one error in regex in .

The Bug

The regex only matches 55 characters total (G + 54 chars), but Stellar public keys are 56 characters (G + 55 chars). The preceding length check on line 33 correctly requires , so the regex was never able to match any valid address — the function was rejecting all valid Stellar addresses.

The Fix

Changed → in the regex, matching the implementation already used in and .

Verification

addr = 'GBUQWP3BOUZX34ULNQG23RQ6F4BVWCIBTLFL2F7HVRQG5LDHNWY2QTWA' // len 56
/^G[A-Z2-7]{54}$/.test(addr) === false  // was: always fail
/^G[A-Z2-7]{55}$/.test(addr) === true   // now: correct

Acceptance criteria (issue #1011)

• Change the regex from {54} to {55}
• Add a unit test asserting a real 56-char G... address returns true (already exists in at line 18)
• Confirm assertValidStellarAddress no longer throws for valid input

Fixes #1011

[ogazboiz]

your regex fix is correct, but the backend CI failure is on backend/src/app.ts:148 which is unrelated to your change — main itself has been red since #977 merged the /version endpoint with a line over prettier's printWidth. i opened #1055 to fix it. once that lands, please rebase and your CI will go green.

git fetch upstream
git rebase upstream/main
git push --force-with-lease

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