feat: add base service layer and Guilds migration pilot

[mishellerv]

Description

Introduces the base services layer for the mobile app's API/networking code
(centralized client, error normalization, retry with backoff, auth
interception) and migrates Guilds as the first feature to consume it, per
issue #218.

Linked Issue

Closes #218

Type of Change

• 🐛 Bug fix (screen or component)
• ✨ New feature / screen
• 🎨 UI/UX improvement
• 📝 Documentation update
• 🔧 Chore / refactor / dependency update
• 🧪 Tests only

Changes Made

• Added a centralized API service layer (src/services/api/): shared HTTP
  client, normalized ApiError type, retry-with-backoff for transient
  failures, response parsing, and an auth interceptor (token injection,
  refresh-on-401, session invalidation on repeated auth failure).
• Added guildsService (src/services/guilds/guildsService.ts) as the first
  feature-level service, wrapping the existing @guildpass/sdk client with
  the new error normalization/retry pattern.
• Migrated useGuilds to consume guildsService instead of calling the SDK
  directly, preserving its public interface and the existing
  GuildNotFoundError export/behavior.
• Adjusted session.adapter.ts / session.types.ts to support a real auth
  contract (token, refresh, invalidate, isAuthenticated) instead of a no-op
  adapter.
• Adjusted React Query defaults (queryClient.ts) to avoid duplicating
  retries now handled by the service layer.
• Documented a pre-existing, unrelated issue (@guildpass/sdk entry
  resolution failure in tests/api.test.ts) and refactor progress in
  docs/KNOWN_ISSUES.md.
• Membership, Access, Notifications, and Attestation are intentionally not
  migrated in this PR — follow-up work, tracked as pending in
  docs/KNOWN_ISSUES.md.

Screenshots / Recordings

Not applicable — this PR is a backend/networking refactor with no UI changes.

iOS	Android
N/A	N/A

Test Evidence

Checklist

• I have read CONTRIBUTING.md
• This PR is linked to an open issue
• pnpm typecheck passes — not run in this environment, please verify in CI
• pnpm lint passes — not run in this environment, please verify in CI
• pnpm test:run passes — all tests green — ran via vitest directly (32/32 passing); pnpm test:run itself was not executed, please confirm in CI
• UI changes include a screenshot or screen recording — N/A, no UI changes
• New screens handle loading, empty, and error states — N/A, no new screens
• NativeWind (Tailwind) classes used — no StyleSheet.create for new UI without justification — N/A, no new UI
• No native modules added that break Expo Go compatibility
• No secrets, keys, or wallet credentials included
• .env.example updated if new environment variables were added — N/A, no new env vars
• Accessibility: interactive elements are keyboard-navigable and have accessibility labels — N/A, no new UI

Additional Notes

• package-lock.json is intentionally not included in this PR, respecting the
  repository's existing decision (commit eef5905) to keep lockfiles out of
  version control.
• Reviewers should specifically check the auth interceptor edge cases (token
  refresh failure, transient errors during retry not invalidating the
  session) and the GuildNotFoundError detection logic (covers both explicit
  404 status and legacy "not found" message matching).

[Lakes41]

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