Add an options page for user-configurable tier score thresholds

[knytcomics-ui]

Summary

The four tier boundaries (20/50/75/100) are hardcoded in src/lib/tiers.ts:10-47 with no way for a user to adjust sensitivity (e.g. a more risk-averse user wanting 'Elevated' to start at 10 instead of 21).

Current Behavior / Relevant Code

• src/lib/tiers.ts:10-53 (TIERS array and tierForScore); no chrome.storage read path exists to override these constants.

Why This Matters

Risk tolerance is inherently personal -- a power user doing frequent, low-value testnet transactions has different needs than someone moving significant mainnet funds; hardcoded thresholds serve neither well by default.

Proposed Solution

• Add a manifest.json options_page (or options_ui) entry and a settings UI for adjusting the four boundary values, persisted to chrome.storage.sync.
• Refactor tierForScore to accept (or read) configurable boundaries while keeping sane, validated defaults (monotonically increasing, 0-100 bounded).
• Update tiers.test.ts to cover custom boundary configurations.

Acceptance Criteria

• Users can adjust tier thresholds via an options page.
• Invalid configurations (non-monotonic, out-of-range) are rejected with clear validation feedback.
• Default behavior (current hardcoded values) is preserved when no customization is made.

Definition of Done

• npm run lint, npm run typecheck, npm test, and npm run build all pass locally and in CI
• New or changed behavior is covered by unit tests (and integration/E2E tests where the change touches interception, background messaging, or the popup)
• Any user-facing or architectural change is reflected in README.md
• No regressions to the existing test suite or existing tier/interception behavior

How to Claim This Issue (Application Process)

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4. Submit a scoped PR. Reference this issue (Closes #<issue-number>), keep the diff scoped to the acceptance criteria above, and ensure all CI gates pass before requesting review.
5. Engage with review. Respond to review feedback within a reasonable timeframe; PRs with no response after 7 days may be closed pending resubmission when you're ready to pick it back up.

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Category: State Management & Extension Lifecycle
Estimated effort: M (medium, ~3-5 days)
Difficulty: Advanced — this issue assumes familiarity with the codebase's MV3 service-worker architecture, the Freighter interception protocol, and/or the Stellar SDK.

[Heazzy500]

Hi, I'm Heazzy 500. My plan is to implement the requested functionality using the project's existing patterns, ensure backward compatibility, cover important edge cases, and provide solid test coverage.

[Primex-hub]

I would love to solve this issue