feat: deploy the canonical Tholos testnet instance

[collinsezedike]

Summary

• Deploys and initializes the canonical, long-lived Tholos testnet instance (contract id in docs/src/DEPLOYMENT.md), using the public-testnet/low-value profile from BOND_SIZING.md: 5 XLM bond, 6 hour challenge window, 1% finalize reward.
• Resolver committee is this repo's existing resolver1/2/3 testnet identities, a stopgap with no real accountability behind it yet, called out explicitly in the docs so it isn't mistaken for a considered choice.
• Rewrites INTEGRATION.md's "deploy your own instance or share one" section: sharing the canonical instance is now the default, a separate deployment is the exception for genuinely incompatible parameters.
• Points demos/freelance-escrow's README at the canonical contract id instead of leaving VITE_THOLOS_CONTRACT_ID's source undocumented.
• Adds a narrow, commented exception to ci.yml's contract-address check for DEPLOYMENT.md's canonical deployment table, the one place a real deployed address should be documented, not scrubbed as if it were stale example code.

Closes #59

Test plan

• Deployed and initialized on testnet, verified live: get_assertion_state for a nonexistent id returns AssertionNotFound, not a dead-contract error
• grep's contract-address check passes locally with the same flags CI uses, confirming the DEPLOYMENT.md exception is scoped correctly and nothing else newly trips it
• mdbook build succeeds with the new DEPLOYMENT.md section and INTEGRATION.md's rewritten anchor link
• No contract source changed, cargo fmt/clippy/test unaffected

[collinsezedike]

Reopening to retrigger CI, no check runs were created for the last push (looks like a dropped webhook, GitHub status page is currently clear).