Improve encounter history, event tracker discovery, and chat TTS

[Zudin987]

Scope

• Reuse the existing offline Encounter History and A/B comparator; no DPS simulator or graph.
• Add observed character-attribute summaries (initial / time-weighted average / last observed / coverage) to saved DPS rows, with backward-compatible serde defaults.
• Capture stats from existing sanitized combat snapshots and avoid inventing unavailable zero or late-capture initial values.
• Add an Attributes tab and same-player A/B stat deltas, retaining existing skill, damage and Imagine comparisons.
• Regression tests for weighting, duplicate samples, boundaries and legacy saves.

Follow-up fixes from Windows CI and review

• Add a checked-in generated-source builder to initialize DpsRow.encounter_attributes, resolving Rust E0063.
• Use a delegated change handler so the Attributes A/B panel continues updating when the comparison player selector recreates itself on each selection; add a regression assertion.

Verification

• Latest head: 40d3676122a0227366ab3ea3c542febe0e72d9b0.
• Windows Rust CI run #805 completed successfully: unit/regression tests, Clippy, native release build, EXE smoke test, size budget, packaging, generated-source diagnostics and native UI render diagnostics.
• Actual in-game packet validation and interactive browser selection checks remain outstanding. Averages are snapshot-sampled rather than exact per-attribute packet timelines; coverage is displayed.

Keep this draft until real-game validation. No release intended yet.