Unify claim status, share fee payment helper, consolidate slug/storage docs

[king-aj-the-first]

closes #337
closes #340
closes #374
closes #382

Summary

Cleanup pass addressing duplicated claim/fee logic and stale docs:

• Claims: Collapse ClaimStatus / ContractClaimStatus into one shared ClaimStatus, add ClaimKind, and route both ownership and contract-address approve/reject paths through apply_claim_decision + transition_to_approved / transition_to_rejected.
• Fees: Extract FeeManager::execute_fee_payment and have pay_fee / pay_registration_fee call it with their storage keys, amounts, and event metadata.
• Slug docs: Merge PROJECT_SLUG_IMPLEMENTATION.md + SLUG_PR_SUMMARY.md into docs/PROJECT_SLUG.md; delete the duplicates.
• Storage docs: Reconcile STORAGE_INDEXES.md with live StorageKey / ExtensionKey usage and explicitly exclude dead scaffolding (DataKey, FeeRefundRecord, FeeConfigHistory*, unused NextProjectId / ProjectLaunchTimestamp).

Changes

Task 1 — Unified claim workflow

• Removed ContractClaimStatus; ContractClaimRequest.status now uses ClaimStatus.
• Added ClaimKind::{Ownership, ContractAddress}.
• Added shared transitions on ClaimStatus and ProjectRegistry::apply_claim_decision.
• Updated approve_claim_request / reject_claim_request and approve_contract_claim / reject_contract_claim to use the shared path.
• Updated contract-claim tests to assert ClaimStatus.

Task 2 — Shared fee payment helper

• New private execute_fee_payment(env, payer, amount, token, paid_flag_key, details_key, event_project_id, operation).
• pay_fee keeps owner-auth, then delegates.
• pay_registration_fee keeps self-auth, then delegates.

Task 3 — Slug docs

• Added docs/PROJECT_SLUG.md (merged canonical doc).
• Removed PROJECT_SLUG_IMPLEMENTATION.md and SLUG_PR_SUMMARY.md.

Task 4 — Storage index docs

• Prefixed documented indexes with live enum paths (StorageKey::… / ExtensionKey::…).
• Added other live Vec-backed indexes used in code.
• Added Dead scaffolding table so indexers do not treat unused keys/types as on-chain.

Test plan

• cargo test claim (ownership claims)
• cargo test issues_242_252_256 (contract-address claims)
• cargo test fee-related tests (pay_fee / registration fee)
• Confirm docs/PROJECT_SLUG.md is the only slug feature doc
• Spot-check STORAGE_INDEXES.md dead-scaffolding list against storage_keys.rs / types.rs

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