t-paliad-168 deliverable 1. Adds a discoverable browse-/learn-mode
entry to the determinator alongside "Etwas einreichen" / "Etwas ist
passiert". Click drops straight into Pathway A's proceeding-tile
picker (navigateToPathway("a")).
The save-to-project CTA disables itself in this mode — extends
isAdhocMode() to also return true when no Step 1 context is set,
mirroring the existing ad-hoc explore behaviour.
i18n keys: deadlines.step2.browse.title / .desc (DE + EN).
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