Add private personalized suggestion ranking

[bartekplus]

Summary

• add a pure, stable personalization policy and ranker over the existing ten-candidate Presage pool
• persist bounded, versioned, per-language acceptance scores in chrome.storage.local
• learn only after successful suggestion acceptance and reverse the exact event on FluentTyper undo
• keep personalization opt-in and bypass ranking exactly when disabled
• add localized settings plus a confirmed Clear learned words action
• exclude learned state from settings import/export and all observability/logging paths
• cover menu and inline promotion, runtime restart persistence, and clearing on Chrome and Firefox

Why

Users repeatedly choose personally useful words that can sit below the visible Presage cutoff. This promotes those existing candidates locally without changing Presage, enabling online learning, adding network behavior, or expanding extension permissions.

Behavior and privacy

• default: off
• storage: local browser profile only, partitioned by resolved language
• learning inputs: successful suggestion acceptances only
• excluded: ordinary typing, document text, text expansions, dynamic templates, ignored suggestions, and arbitrary out-of-pool words
• limits: 500 words per language and 100 recent event IDs
• disabled ordering remains byte-for-byte identical to the previous path

Validation

• bun run check
• bun run test (1,558 main tests plus isolated suites)
• bun run test:e2e (Chrome: 26 passed)
• bun run test:e2e --platform=firefox (Firefox: 26 passed)
• bun run check:e2e:coverage (77 behaviors)
• bun run test:e2e:full (Chrome: 65 passed, 7 development-only skipped)
• bun run test:e2e:full --platform=firefox (Firefox: 65 passed, 7 development-only skipped)
• bun run build
• bun run build --platform=firefox
• enabled ten-candidate ranker microbenchmark: about 14.5 microseconds/call locally; disabled mode bypasses snapshot access and sorting

Closes #361

[chatgpt-codex-connector]

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