Document cache key format and TTL precedence rules

[Joyful12-tech]

Summary

This PR adds documentation for exact cache key formats and TTL precedence rules, as requested in #392.

Changes

docs/cache-adapters.md

• Key Composition (new section): Lists the exact cache key template for every cached service method (checkAccess, checkRoleAccess, getMembership, getRoles, getUserRoles, getGuild, getGuildConfig), verified against the actual source in src/client/GuildPassClient.ts.
• TTL Precedence (new subsection): Clarifies that only the client-level cacheTtl applies, with a concrete worked example.
• Fixed inaccurate claim: The previous docs stated that "methods that accept a per-call override subtract elapsed time from the deadline before storing." This is incorrect — there is no per-call TTL override in the current implementation (withCache always passes this.cacheTtl). The text now accurately reflects the source.
• Added a note that the wallet: prefix is an invalidation-only namespace.

docs/sdk-guide.md

• Added cross-link to the new Key Composition section.

docs/architecture.md

• Added cross-links to the Key Composition and TTL Precedence sections under the Caching Layer bullet.

Discrepancy noted

The issue's acceptance criteria asked for a worked example with a per-call TTL override. No such override exists in the current implementation — RequestOptions carries timeoutMs, retry, and signal but no cacheTtl field, and withCache() always uses the client-level cacheTtl. The documentation reflects this accurately rather than inventing a feature.

Closes #392

[Lakes41]

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