Conversation text is still only persisted when explicitly saved (⌘S),
but tokens/cost/model/provider are now logged to a new usage_events
table for every completed AI response regardless — the Analytics
view now reads from this table instead of messages, so it reflects
real usage even for conversations that were never saved. Adds a
By Provider chart mode alongside Over Time/By Model.
Also fixes the Analytics entry point: ToolbarItem(placement: .navigation)
silently doesn't render in a plain .sheet-presented NavigationStack on
macOS. Moved the button inline next to the segmented picker, matching
the codebase's existing convention (e.g. the model-favorites star filter).
New large modal off the Stats sheet with a 6-way timeframe picker
(Today/7 Days/Week/Month/Year/Total), three tappable summary tiles,
and native Swift Charts (bar chart over time, pie chart by model).
Backed by date-range-filtered DatabaseService queries plus a new
daily-bucketed query — no schema changes needed since messages
already carry timestamp/tokens/cost/role.
rune