feat(panel): add insights overview to the outcomes tab

[StuBehan]

What

Adds an Insights overview and folds it in with the existing per-ticket view as one Outcomes tab (⌘4), so usage and outcomes live together. No new capture: it reads the same handoff ledger plus the per-branch outcome/PR state the ticket view already computes, so the two agree by construction.

The Outcomes tab (two panes)

Lands on the Overview (the aggregate); → carousels into the Tickets list, ← back (mirrors the Usage tab's pane carousel). Settings stays at ⌘5.

Overview (a scroll page: ↑↓ scroll, ⌘↑↓ jump, W cycles the window):

• Shipped share headline: of the tokens spent in a trailing window (24h / 7d / 30d / 90d), how much sits on merged/pushed work versus in-flight versus abandoned (committed/needs-review gone quiet for over 14 days).
• Spend bar partitioning tokens across those three buckets.
• Top tickets by spend: the heaviest tickets/repos with their dominant outcome; click a row to open the ticket (STACKNUDGE_TICKET_URL) or its PR.
• Agents: the token mix plus each agent's shipped share (whose work actually merges), and a Models mix rendered as shortened, wrapping pills.

Tickets: the existing per-ticket rollup, unchanged, now reached with → / ←.

Design notes

• Insights.summarize(...) is pure (no I/O) and unit-tested; it rolls up over the ledger plus the outcome/PR maps.
• Extracted OutcomeWatcher.effective(local:pr:) so both panes share one "did it ship?" definition (a squash-merged branch reads shipped in each).
• Promoted the model-name shortener to a shared ModelName.short (used by Sessions and Insights) and added a small FlowLayout so the model pills wrap instead of compressing.
• Token-only for now (contextTokens, the same effort proxy the ticket view shows); per-model dollar cost and reclaimed-time are planned follow-ups.

Testing

• InsightsTests: bucket math, shipped-share, the staleness cutoff, PR-supersedes-local, top-tickets ranking and dominant-status precedence, per-agent shipped share, window boundary, and empty/nil cases.
• scripts/typecheck-tests.sh is green; assertions were verified locally via an in-module harness (swift test needs Xcode, so CI runs the real suite).