fix(app) internal/external link handling

[alexyaroshuk]

Fixes #10613, #8361

What does this PR do?

fixes the external link handling issue that was reverted in #10697

The previous implementation broke internal app navigation (sessions, settings,
etc.) because it opened ALL links externally, regardless of whether they were
internal or external to the app.

Now properly distinguishes between internal and external links by comparing
origins.

Changes

1. Desktop app: Fixed link interception to use origin comparison
2. Web app: Added external link interception (opens in new tab)
3. Tests: Added e2e test file

How did you verify your code works?

Tested in a dev desktop build, dev web build, and in a release desktop build

[github-actions]

Hey! Your PR title Fix/link handling doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

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

No duplicate PRs found

[adamdotdevin]

@alexyaroshuk can we not do something more similar to our previous approach by modifying the new markdown parser to add a class to markdown created anchors? I'm hesitant to take any other approach.

[alexyaroshuk]

@alexyaroshuk can we not do something more similar to our previous approach by modifying the new markdown parser to add a class to markdown created anchors? I'm hesitant to take any other approach.

right on, please check #10816