Polish thread reply hover states

[klopez4212]

Summary

• Keep direct children aligned with the thread head; start indentation/connectors at grandchildren.
• Add hover grace for profile/timestamp popovers and keep thread action trays from being clipped.
• Keep inbox hover paint off the scrollbar edge without adding a layout gutter.

Validation

• Code checks: no changed-line findings.
• pnpm exec biome check ...
• pnpm exec tsc --noEmit
• pnpm test (1194 tests)
• just desktop-build
• git push pre-push hook: desktop-test, rust-tests, mobile-test, desktop-tauri-test
• just ci is blocked by an existing origin/main Tauri clippy lint in desktop/src-tauri/src/managed_agents/runtime.rs (manual_contains).

Screenshots

Thread connectors

Inbox hover edge

[chatgpt-codex-connector]

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Reviewed commit: 1bbd0cc479

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