Feature/share based accounting

[nonso7]

Closes #355

[ogazboiz]

The contracts CI is failing on the rustfmt format check. This isn't a logic issue, just formatting.

Run this in the contracts directory and push:

cd contracts
cargo fmt

Then commit and push the formatting changes. The CI should pass after that.

[ogazboiz]

hey @nonso7, the diff on this PR is over 20,000 lines which is way too large for a single review. could you break this into smaller, focused PRs? for example:

• one PR for the share-based accounting contract changes
• one PR for the test updates
• one PR for any frontend/backend integration

massive PRs are really hard to review properly and tend to sit open for a long time. smaller ones get merged faster.

also, no CI checks ran on this branch. you'll want to trigger a fresh run after splitting.

[ogazboiz]

The codebase issues on main have been resolved and all CI checks are passing now. Please rebase your branch to pull in the latest changes before continuing. Thanks for your patience.

[ogazboiz]

Same blockers as #525: rebase, renumber migrations above 1783000000013, remove debug files. Shares identical backend changes with #525, so one should merge first and the other rebase on top.

[ogazboiz]

heads up, a few important changes just landed on main that affect your PR:

1. axios pinned to 1.13.5 - there's an active supply chain attack on axios 1.14.1 (pulls in confirmed malware). we added overrides in all package.json files to block it.

2. CI now runs a supply chain audit before backend/frontend jobs. if your lockfile has a compromised package, CI will fail with a clear error.

3. backend test fixes - loanEndpoints tests now use valid Stellar addresses and base64 strings. if your PR was failing backend CI but you didn't touch backend code, this should fix it after rebase.

please rebase on latest main:

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