feat: add structured errors, recovery workflows, and read caching

[investify2826-ctrl]

Summary
This PR delivers four Sorokit improvements for safer account recovery, more actionable failures, and efficient read-only Soroban calls.

Changes
Add structured error categories, sanitized operation context, and actionable recovery guidance while preserving existing error codes.
Add guardian/delegated recovery workflows with validated contacts, approval thresholds, time locks, cancellation, expiry, replay protection, and private-key-free progressive signer replacement plans.
Add network-scoped read-result cache keys, configurable TTL support, explicit per-request cache bypass, deterministic invalidation, and regression coverage while retaining successful-only caching and concurrent deduplication.
Propagate the structured error model through existing account, network, token, and public package APIs.
Validation
Focused Vitest suites: 54 tests passed.
git diff --check passed.
Full typecheck remains blocked by pre-existing unrelated errors in NFT metadata, transaction bundles, and price subscriptions.
Closes #465
Closes #467
Closes #477
Closes #478

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