feat: establish native iOS foundation

[andrewmuratov]

Summary

Establishes the first coherent native Swift/SwiftUI foundation for Gapwise for UTM.

This PR turns the repository from a branding/bootstrap shell into a real iPhone application foundation while keeping the current product scope UTM-only and following the boundaries already established across the Gapwise ecosystem.

Included

• native SwiftUI app target and shared scheme
• Today, Timetable, Gaps, Map, and Settings navigation surfaces
• local .ics timetable import with review-before-save
• deterministic timetable reconciliation and schedule arithmetic
• local persistence behind explicit repository boundaries
• portable Foundation domain/import logic with fixture-driven tests
• conservative UTM campus integration boundary with no invented map geometry, entrance, routing, or accessibility facts
• Linux-portable Swift validation plus macOS/iOS CI
• README updated to describe the actual UTM-only product scope and current implementation truthfully

Architecture / trust boundaries

• Gapwise-for-UTM/gapwise remains authoritative for canonical product/timetable/gap/routing semantics.
• Gapwise-for-UTM/data remains authoritative for canonical UTM campus facts, geometry, provenance, entrances, and uncertainty.
• this repository owns native iOS presentation, local timetable handling/persistence, app lifecycle/state, and Apple-platform integration.

Legacy/off-campus campus values may remain decodable/detectable so imported source data is not silently corrupted, but this PR does not claim a UTSG, UTSC, or mixed-campus product experience.

Validation

The portable core is configured to run under Swift 6.3.3 on Ubuntu Noble, while the Apple-only application path is validated separately on macOS/iOS CI. No Linux-only workaround is used to fake SwiftUI or Apple SDK validation.

Merge only after the PR checks are green.