[Task] Replace use-session-hash-scroll source snapshot with behavior test

[Astro-Han]

Goal

Replace the use-session-hash-scroll source-string snapshot assertion with a behavior test for the hash-scroll contract.

When this is done, Windows advisory CI should no longer fail because of LF/CRLF differences, and the test should verify behavior instead of source-code shape.

Scope

In scope:

• Replace the source-code toContain() assertion in use-session-hash-scroll.test.ts with a behavior-focused test.
• Cover the hash-scroll contract:
  • when the URL hash points to an already-rendered message, the code scrolls to that message directly
  • it does not call onMessageNavigation
  • it does not emit duplicate navigation for the same already-rendered message path

Out of scope:

• Do not only normalize CRLF as the final fix unless a temporary release unblocker is needed.
• Do not introduce AST parsing just to keep testing source shape.
• Do not change product behavior.

Relevant files or context

Problem:

• Windows advisory CI fails in unit-windows-app because use-session-hash-scroll.test.ts reads source code and checks an LF-only string with toContain().
• On Windows, source content can include CRLF, so the assertion fails.
• This is not a product regression and not introduced by feat(sidebar): project rename and remove from sidebar #517. It exposes test debt: the test verifies implementation shape instead of behavior.

Likely file:

• packages/app/src/pages/session/use-session-hash-scroll.test.ts

Verification

• Run the targeted unit test that covers use-session-hash-scroll.
• Confirm the test passes on Windows advisory CI.
• Confirm the new test fails if the already-rendered-message hash-scroll path incorrectly calls fallback navigation.

Execution mode

Agent can implement directly.