feat(meridian): chore-replace-panic-with-typed-errors-in-router-

[Caneryy]

Closes #433

Summary

• [Chore] Replace panic! with typed errors in router and adapter contracts

Test plan

• Relevant tests pass locally
• Manual verification on affected UI or API paths

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[collinsezedike]

CI is failing on two things:

1. Commit Messages: header is 73 characters, over the 72-char limit. Needs shortening, e.g. chore(contracts): replace panic! with typed errors.
2. Soroban Contract Tests: cargo fmt --all -- --check fails on the import block in blend-adapter/src/lib.rs. Run cargo fmt and push the result.

The PR title (feat(meridian): chore-replace-panic-with-typed-errors-in-router-) also needs fixing to match, since this repo squash-merges using the PR title as the commit message.

The implementation itself is correct, I ran the full test suite and clippy locally and both pass clean. Just these two fixed before merge.

[collinsezedike]

This PR's body doesn't follow CONTRIBUTING.md's PR body format (see "Pull Request Process" > "PR body format").

The Summary section should describe what changed and why, not restate the issue title. The Test plan checkboxes should be checked once you've actually run pnpm lint && pnpm typecheck && pnpm test locally, and the second line should say what you manually verified, not generic placeholder text.

Please update the PR body to reflect what you actually did and verified before this is merged.