chore: consolidate and migrate native-apps/unity_ii to icp-cli

[marc0olo]

Closes #1347.

Summary

• Consolidates unity_ii_applink and unity_ii_universallink into unity_ii_deeplink (single canonical example)
• Migrates from dfx to icp-cli: replaces dfx.json + webpack with icp.yaml, mops.toml, and Vite
• Ports frontend to @icp-sdk/auth v7 + @icp-sdk/core v5.3 — no @dfinity/* packages remain
• Fixes duplicate-check bug in AndroidPostBuildProcessor.cs (was already in the applink variant but missing from deeplink)
• Makes Unity canister fields configurable via Inspector (removes hardcoded mainnet IDs, adds icGateway for local device testing)
• Adds test.sh, CI workflow, and consolidated README documenting local vs. mainnet testability for all three URL-scheme variants

Key decisions

Double-delegation bridge — preserved intact; educational value depends on it.

No local II deployment — icp.yaml has no ii: true. The frontend hardcodes https://id.ai/authorize (the default in @icp-sdk/auth v7). icp-cli ≥ 0.2.4 trusts mainnet BLS signatures on the local replica, so delegations from mainnet II work locally.

SDK migration (@dfinity/* → @icp-sdk/*):

• AuthClient.create({identity}) + login({onSuccess}) → new AuthClient({identity}) + signIn()
• ECDSAKeyIdentity, DelegationChain, Ed25519PublicKey from @icp-sdk/core/identity
• safeGetCanisterEnv() from @icp-sdk/core/agent/canister-env

Motoko: mo:base/Principal → mo:core/Principal (matches AGENTS.md and who_am_i)

What can be tested locally

Step	Testable locally?
II login (mainnet II in local browser)	✅
Deep link internetidentity:// callback	✅
Backend call with delegation identity	✅
Android App Links (HTTPS scheme)	❌ (requires deployed assetlinks.json over HTTPS)
iOS Universal Links	❌ (requires Apple dev account + HTTPS AASA)

Test plan

• icp network start -d && icp deploy && bash test.sh passes in the native-apps/unity_ii_deeplink directory
• Frontend builds without errors (npm run build --prefix frontend)
• CI workflow passes (triggers on PR paths)
• Full end-to-end test on a physical device via local deployment (see README "Testing locally" section)
• Mainnet deployment with icp deploy -e ic and Unity Inspector updated with deployed canister IDs

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