Improve RSVP thought flow and retire legacy grouping

[Steadyx]

What changed

RSVP now coordinates grouping, emphasis, timing, replay, and peripheral context around shared phrase boundaries. Dense phrase endings receive bounded integration holds; replay follows the current or preceding phrase, resume preparation reflects pause length, and context cues remain stable within a thought.

Scored segmentation is now the sole grouping engine in debug and release for every language, including missing language metadata. Remove LEGACY_GREEDY, the strategy switch, and rollout gates. Navigation, previews, and pace estimates use the same engine; language-specific evidence stays gated by language, and single-word reading remains available through the existing setting.

This targets the next version after 1.3.0; no release version bump is included.

Risk

Changes affect RSVP grouping, exposure timing, replay, and context transitions. Regression coverage preserves source ranges, split-word resume cursors, punctuation boundaries, preview limits, and cache identity. Tiny previews retain visible content without exposing scorer lookahead. Saved grouping widths are bounded by the six-word scoring horizon.

Automated checks do not establish comprehension gains or validate physical-device rendering. Connected instrumentation and a dedicated device reading/visual pass were not run for this branch; multilingual rendering and sustained reading remain qualification items. Synthetic pace estimation currently uses an English sample.

Validation

• ./gradlew qualityCheck
• ./gradlew qualityGate — 742 tests, zero failures/errors/skips; debug APK assembled
• Android Lint — zero issues
• ./gradlew :app:compileReleaseKotlin
• Focused regression tests added or updated for thought timing, replay/context, language policies, saved widths, previews, and source cursors
• git diff --check
• Connected instrumentation and physical-device visual qualification — not run for this branch

Validated at 70975df with JDK 17.

Quality policy

• No baseline, ignoreFailures, broad exclusion, or unrelated threshold relaxation was added
• No new suppressions
• No generated files, debug logging, commented-out code, or unrelated formatting churn is included