[Docs/Tooling] Add deployment manifests with contract IDs

[Jayrodri088]

Complexity / points: Medium (150 points) - maintainer label: points-150-medium

PR must include:

• Closes #30 in the PR description
• Tests added or updated where behavior changes
• Docs updated if public API, lifecycle, or deploy steps change
• No unwrap() in production Soroban contract paths (project convention)
• cargo test passes locally; match CI (cargo fmt, cargo clippy -D warnings) when touching Rust

Problem

The root Readme.md includes placeholders for contract addresses (testnet and mainnet), but the repo does not contain a machine-readable deployment record.

As the project progresses from infancy to a complete workflow, contributors and scripts need a consistent source of truth for:

• contract IDs per network
• initialization parameters used

Without this, each contributor redeploys (wasting time) and setup becomes error-prone.

Proposed change

Add a deployment manifest file (and optionally a simple loader in scripts) that records deployed contract IDs per network.

Acceptance criteria

• Add deployments/ directory (or equivalent) with at least testnet.json
• Include entries for:
  • invoice-escrow
  • invoice-token
  • payment-distributor
• Include metadata: network name, timestamp, and initialization params (platform fee bps, admin, etc.)
• Update deployment docs/scripts to use this file (especially once scripts from Issue 11 exist)
• Values can remain placeholders until real deployments are available, but the structure must be complete

Dependencies

• Depends on [Tooling] Add deployment + initialization scripts (Issue 11) ideally, but the manifest structure can be added now.
• Depends on .env.example for variable naming conventions (Issue 9)

[Jayrodri088]

Deferred (Wave 1 scope)
Maintainers are focusing this wave on implementation: escrow, invoice-token lifecycle, settlement/payment flows, payment-distributor, tests, and security bugs — aligned with decentralized invoice factoring on Stellar (liquidity for sellers, yield for investors, on-chain escrow/settlement).

Documentation issues will be reopened or recreated in a later wave. If you already started work, comment here and we can link a follow-up issue.