fix(harmonyos): align collapsed header actions to edges

[wgqqqqq]

Summary

• let the collapsed conversation Header span the full detail viewport
• place the restore and overflow actions on the physical 16vp Header gutters
• keep the timeline and Composer independently centered and width-constrained
• update the wide navigation design contract

Context

Follow-up to #2492. That PR made the leading and trailing actions symmetric, but both still lived inside the centered 920vp route shell. On a fully unfolded triple-screen viewport, the shell added about 109vp of outer inset on each side. The Header now spans the detail viewport while timeline and Composer retain their own 800vp and 760vp limits.

Verification

• pnpm run harmony:architecture
• HarmonyOS LocalTest
• assembleHap
• installed and launched on Huawei_TripleFold emulator
• triple-screen collapsed Header margins: 46px leading / 45px trailing in a 3184px viewport
• triple-screen Composer center: 1592.5px
• dual-screen collapsed Header margins: 46px leading / 45px trailing in a 2048px viewport
• dual-screen Composer center: 1024px
• verified a populated local conversation in triple-screen and dual-screen collapsed modes

Remote scenarios

• local simulator exercised
• remote workspace, remote control, Peer Device Mode, and Detached Dispatch were not exercised; this change only adjusts the shared HarmonyOS presentation container