Apply the four Agentation notes about desktop sizing: reduce the Issues/PR navigation icons from 18px to 16px, add 8px between channel access controls and the new-tab button, and use the tabs' 12px text size throughout Channel details. Clamp the summary to four lines with an ellipsis.

Closes #210.

Validation: type checks, formatting, oxlint, and production app build pass. Local formatting/lint excludes the pre-existing native recovery backup; plain `bun run ci` scans that backup's third-party files (recorded in #173). React Doctor reports only the existing SessionDetailsView complexity warning. Verified the refreshed native 1100×760 window with the user's real long summary, the four-line ellipsis, smaller text/icons, added gap, and working new-tab menu. The existing composer draft survived the window refresh.

### Built in Ace

Checks, build, and GitHub operations used the real `annotation-polish` Ace channel terminal. Code edits and review used Codex because Ace cannot host this external harness yet (#9). Native visual verification used Codex computer use because this harness cannot directly use Ace's channel-native controls (#9, #73). The running Ace-dev app was refreshed and left open with the changes.