feat(settings): nudge when runtime permissions aren't all granted

[StuBehan]

Problem

When a runtime grant (Accessibility, Automation → System Events, or Notifications) isn't set, StackNudge silently loses core behaviour — no banner, no window focus, no Enter-to-approve keystroke — with nothing in the panel to say why. The only way to notice was to open Settings → Check permissions… and look.

Changes

Surfaces missing permissions the same way updates already are — an at-a-glance dot plus a pinned banner:

• Orange dot on the Settings tab. tab() now takes dotColor: Color? instead of dot: Bool; the Settings tab shows orange when a grant is missing, the existing accent dot when only an update is pending (permissions win the colour — they're more urgent).
• permissionsRow() banner pinned above the Settings sections when any grant is missing. Lists which ones (e.g. "Accessibility, Automation") and, like the update row, is keyboard-navigable — selecting + Enter (or a click) opens the Permissions window.
• State + refresh on PanelNav: missingPermissions: [SettingsPane] and refreshPermissions() (Accessibility/Automation probed sync, Notifications async). Both denied and not-yet-determined count as missing. Refreshed on launch and on every Settings open, so the dot + banner clear once the user grants and comes back.
• Fix: updateRow hardcoded .id(0) / selectedSettingIndex = 0, assuming it was always the first row. Now uses nav.index(of: .update) so it survives the permissions row sitting above it.

Testing

• swiftc -typecheck panel/*.swift shared/*.swift — clean.
• Added test_permissionsRow_prependedWhenMissing and test_permissionsRow_sitsAboveUpdate_whenBothPresent to SettingsRowTests.
• Verified live: revoking a grant shows the orange dot + banner; granting and returning to Settings clears both.

Follow-ups (not in this PR)

• The banner is a static list; it doesn't yet distinguish denied from not-yet-determined in the copy (both read the same).

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