feat: rule-based on-call scheduling with Schedule tab (#21)

[wiseelf]

Summary

• Adds RecurrenceRule + ScheduleException models to TimeTrackerCore — supports day-of-week patterns and interval+duration cycles (e.g. every 3 days, 1 week on / 1 week off)
• New Schedule tab in the on-call view: define a rule, browse a month calendar pre-filled with on-call days, tap any day to skip it or override its hours
• Billing engine (OnCallBilling) now evaluates rules and exceptions alongside existing rotation blocks; existing callers compile unchanged (new params default to [])
• OnCallStore persists rules and exceptions with backward-compatible JSON decoding
• 37 tests pass: 10 RecurrenceRuleTests, 6 RecurrenceBillingTests, 21 existing OnCallBillingTests
• Fixes bug where reopening the app after clicking outside the settings panel would land on Settings instead of the main page

Follow-up fixes and improvements (post-initial review)

• Fix: calendar day cells were not tappable — .contentShape(Rectangle()) added to DayCell to make clear-background cells hit-testable
• Fix: DayDetailPanel was clipped below fold — removed ScrollView/scrollDisabled from ScheduleTab so ContentView's GeometryReader reports natural height and the window auto-expands
• Feat: global week-start-day setting (weekStartsOnMonday on OnCallSettings); all day-of-week UIs (calendar grid, rule editor, rotation editor, non-billable add row) respect it
• Feat: inline rate editing in settings — pencil button opens an edit row per entry (date picker + text field + save/cancel)
• Feat: non-billable add form hidden behind a + toggle button; shown on demand
• Feat: passive/active multiplier fields replaced with free-form TextField (commit on blur/return, validated 0–200%, @FocusState for blur detection)

New files

• Sources/TimeTrackerCore/RecurrenceModels.swift
• Sources/TimeTracker/RuleEditSheet.swift
• Sources/TimeTracker/OnCallCalendarGrid.swift
• Sources/TimeTracker/ScheduleTab.swift
• Tests/TimeTrackerTests/RecurrenceRuleTests.swift
• Tests/TimeTrackerTests/RecurrenceBillingTests.swift
• docs/adr/0001-schedule-tab-for-rule-based-on-call.md

Test plan

• swift test — all 37 tests pass
• swift build clean
• On-call tab shows Week / Month / Schedule segments
• Schedule tab: + button → Add Rule sheet (day-of-week and interval modes, day toggles, time pickers, anchor/end date)
• Saving a rule shows it in the rule row; calendar highlights generated days
• Tap a highlighted day → detail panel opens (window auto-expands); on-call toggle + time pickers work
• Toggle off adds skip exception (day un-highlights); toggle back removes exception
• Edit hours → "Reset to rule defaults" appears; clicking restores rule times
• Week/Month tabs keep independent offsets; summaries include rule-generated days in totals
• Settings: toggle "Week starts on Monday" → all day pickers reorder (calendar headers, rule editor, rotation editor, non-billable form)
• Settings: pencil on rate entry → inline edit; save updates the entry
• Settings: + next to "Non-billable window" shows/hides add form
• Settings: type a value like "41" or "92" into passive/active field → committed on blur/return
• Reopen app after clicking outside → lands on main page (not Settings)