feat(claimable-balance-readiness): evaluate claim eligibility from Horizon predicates

[chainsmt]

Closes #465

Summary

Adds a self-contained Claimable Balance Claim Readiness feature under features/claimable-balance-readiness/. It answers a narrow question: at a user-chosen UTC time, does this named claimant appear eligible to claim this existing claimable balance — and why — without ever building or submitting a claim transaction.

Horizon is only used to load GET /claimable_balances/{id}. Predicate evaluation is entirely local.

Motivation

Horizon already returns claimants and nested predicates, but the UI did not explain branch-by-branch readiness at an arbitrary evaluation time. Relative predicates also need creation-time context; guessing that context produces false yes/no answers. This slice makes that uncertainty explicit as indeterminate.

What this PR does

• Validates balance ID and claimant (G…) before any Horizon call (invalid_balance_id, invalid_claimant, invalid_time).
• Normalizes nested predicates in lib/predicate-tree.ts and evaluates them in lib/claim-evaluator.ts for:
  • unconditional
  • absolute before/after
  • relative before/after
  • AND / OR / NOT
• Resolves relative-time context from the balance creation/last_modified_time path in lib/time-context.ts. If that context cannot be established reliably, returns indeterminate instead of inventing an answer.
• Distinguishes:
  • balance_not_found (Horizon 404 / missing resource)
  • found balance where the address is simply not listed as a claimant (ineligible / not a claimant)
  • eligible / ineligible / indeterminate verdicts from the selected claimant’s tree
• Renders the full claimant list, nested predicate tree, and readiness verdict with explanations exposed to screen readers (branch-by-branch).
• Maps transport/decode failures through claimableBalanceReadiness.errors.ts into actionable copy.ts strings (unsupported_predicate, request_failed, etc.).
• Ships the full RevyHub feature contract: schema, hook state machine, panel/form/result/empty UI, MSW handlers, fixtures, unit + a11y + e2e specs (including an indeterminate journey).

Architecture notes

• Slice-only PR: all changes stay inside features/claimable-balance-readiness/. Registry routing is generated; no shared navigation edits.
• Uses Result<T, Code> for expected failures; user-facing English lives only in copy.ts.
• Amounts remain string/BigInt-safe where displayed; secrets are never accepted.

Acceptance criteria coverage

• Validate balance ID and claimant before the request
• Evaluate unconditional, absolute-time, relative-time, AND, OR, NOT
• Show selected evaluation time and creation-time context used for relative predicates
• Explain ineligible claimant separately from a missing balance
• Expose full branch-by-branch explanation to screen readers

Out of scope

• No claim operation creation, signing, or submission
• No wallet / private key ownership
• No changes outside this feature directory

Test plan

• npm run verify:features -- claimable-balance-readiness (35-file contract)
• npm test -- features/claimable-balance-readiness (55 tests)
• Manual: /tools/claimable-balance-readiness — eligible claimant path
• Manual: address not on claimant list vs 404 balance
• Manual: relative predicate with missing creation time → indeterminate

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