fix(atlas): wire the canvas Initialize button to the deterministic endpoint (#114)

The 'initialize this project's graph' button dropped '/initialize-atlas-graph'
into the chat composer and sent it, delegating graph creation to the AGENT —
inheriting every fragility of the prompt path (skipped when the atlas binary
is absent, or on short tasks). Meanwhile initGraph(), which calls
thesisAPI.initProject → POST /api/thesis/project/init (the proven
find-or-create endpoint) and then refetches + selects the new root, was
defined but wired to nothing, and busy={initializing()} was dead.

Point the primary button at initGraph() so it deterministically creates the
graph without the agent or the atlas binary, and surfaces a typed error toast
on failure. The secondary 'chat' action still drops the skill invocation for
review when the user wants to resolve a plan/auth issue in chat.