fix(subdirectory): reorder navigationUtils so primitives precede helpers

oxlint's `no-use-before-define` rejects function-declaration hoisting:
`redirect()` calls `navigateTo()` declared further down in the file, and
the rule fires on the call site even though the runtime ordering is
sound.

Moves `navigateTo` and `navigateWithState` to the top of the module
(directly after imports) and removes the corresponding "Legacy multi-mode
helpers" section that previously held them at the bottom. The channel-3
section now follows and can reference the primitives in textual order.
Section comment updated to explain the placement.

Also extracts the long template-literal expression in `getShareableUrl`
into a `safePath` local so the line fits under prettier's print width.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>