fix(app): resume sessions in desktop app

[anduimagui]

Summary

• wire the app session route through the existing session resume lifecycle so desktop resumes existing sessions when reopening them
• skip the first resume call for brand-new sessions and fresh forks so only true reopen flows trigger resume
• add focused unit coverage for the shared app resume helper

Notes

• this depends on feat(session): add session.start lifecycle hook #18007 and is intended to be reviewed after or alongside it
• because the base branch cannot live in anomalyco/opencode without push access, this upstream PR includes the full #18007 stack plus the desktop follow-up

Verification

• bun test src/pages/session/session-resume.test.ts (blocked in this checkout because packages/app/happydom.ts imports missing @happy-dom/global-registrator)
• bun typecheck in packages/app (blocked in this checkout by existing workspace dependency resolution issues)

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found one potentially related PR:

#18007: feat(session): add session.start lifecycle hook

This PR is related because:

• PR fix(app): resume sessions in desktop app #19157 (the current PR) explicitly depends on feat(session): add session.start lifecycle hook #18007 as noted in the description
• feat(session): add session.start lifecycle hook #18007 adds the session.start lifecycle hook that fix(app): resume sessions in desktop app #19157 uses to wire up the session resume flow in the desktop app
• They are meant to be reviewed together or in sequence

No other duplicate PRs were found. The other search results (like #19116 on reconnect logic and #7756 on session delegation) address different aspects of session management but are not duplicates of this specific fix for resuming sessions in the desktop app.

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