fix(desktop): align notifications inbox row timestamps and action buttons

[janicduplessis]

Description

The Notifications inbox row's trailing action Button sized to its own label ("Open workspace" vs "Show device" vs "Open pull request"), so the timestamp next to the title shifted horizontally row to row. .top alignment also left the button reading as vertically centered against the top-pinned dot and icon, while the timestamp sat flush with the title line. Maintainer report: "Can we have better alignment here."

Before:

Solution

In InboxRow (apps/desktop/Sources/StimDesktop/Views/InboxView.swift):

• Fixed-width action-button column, sized to the widest of OversightTarget's six possible labels (Notices.swift's new actionTitles) via a ZStack of hidden Text views in the button's own font/padding, so it tracks the app's font instead of a hardcoded point width.
• Timestamp moved out of the title HStack into its own trailing group, right before the button. With the button now fixed-width and nothing following it, the timestamp's trailing edge lands at a constant x for free, no explicit frame needed.
• Row HStack switched from .top to .center, dropping the .padding(.top, ...) hacks that had approximated baseline alignment. Dot, icon, timestamp, and button now all center on the row's two-line text block.

Test plan

Built and ran a Stim Desktop test copy on the Mac mini, seeded with entries covering all six action labels, read/unread rows, and a quiet-hours entry (longer "9:45 AM · Quiet hours" detail text). Verified:

• Timestamps and buttons line up across rows regardless of label or detail-text length, light and dark.
• Clicking a button still opens its target and marks the row read; a live notification that arrived mid-test slotted into the same aligned layout.
• At 700 pt window width, titles and subtitles truncate with an ellipsis while the timestamp and button columns hold their position.

After, light:

After, dark:

After, 700 pt width (title/subtitle truncation):

swift build and swift test (including InboxTests) pass.

Fixes #1831