refactor: optimize browser resolution by using direct Get call (#51)

Optimizes `resolveBrowserByIdentifier` to use the direct `Get` API
endpoint instead of listing all browsers and searching through them.

Related:
[KERNEL-649](https://linear.app/onkernel/issue/KERNEL-649/cli-resolvebrowserbyidentifier-should-use-the-api-endpoint)
and blocked by onkernel/kernel#790

Tested `kernel browsers delete` works with both session id and
persistent-id and it works!

Also took some time to improve how errors are printed! In some places in
code we use `pterm.Error` and then `return nil` and in others we just
`return err`. Now we can update everything to just `return err` and the
ErrorHandler wrapper will take care of printing with consistent styling.



<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Refactors browser resolution to use direct `Get` everywhere, removes
legacy lookup helpers, centralizes CLI error handling via Fang, and
updates tests accordingly.
> 
> - **CLI — Browsers**:
> - Replace all `resolveBrowserByIdentifier`/pagination lookups with
direct `b.browsers.Get(...)` across delete, view, get, logs, replays,
process, fs, computer, extensions.
> - Remove legacy helpers `listAllBrowsers`, `safeGetNextPage`, and
`resolveBrowserByIdentifier`.
> - Behavior change: surface errors (e.g., not found) instead of
printing and returning nil in many paths.
> - **Root/Error Handling**:
> - Add Fang `WithErrorHandler` to wrap errors with
`util.CleanedUpSdkError` and print consistent error styling + `--help`
hint for usage errors.
> - **Tests**:
> - Update fakes to default `Get` -> error on not found; add
`newFakeBrowsersServiceWithSimpleGet()` helper.
> - Adjust expectations to assert returned errors (not printed messages)
and use direct `Get` flow in all tests.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
4da6355. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: tnsardesai