Fix incorrect TIS class-period time mapping used by ICS and reminders

[Stevvven777]

The TIS calendar/reminder implementation uses an incorrect class-period mapping from period 5 onward and accepts nonexistent periods 12-13.

Verified against the SUSTech “上课节次时间查询” PDF:

• P1 08:00-08:50
• P2 09:00-09:50
• P3 10:20-11:10
• P4 11:20-12:10
• P5 14:00-14:50
• P6 15:00-15:50
• P7 16:20-17:10
• P8 17:20-18:10
• P9 19:00-19:50
• P10 20:00-20:50
• P11 21:00-21:50

Current code starts P5 at 13:30, P7 at 15:30, P9 at 18:00, and defines P12/P13. This shifts generated ICS events and current/next-class reminders.

Acceptance criteria:

• Update the canonical mapping to P1-P11 above.
• Reject unsupported P12/P13 values where time conversion is required.
• Update regression tests for ICS generation and live period lookup.
• Keep timetable planning ranges aligned with the supported TIS periods.

[Stevvven777]

Verified the supplied “上课节次时间查询” PDF against current origin/main. The affected installed version is v0.8.4, while the code fix was already merged in #11 (commit 8faee85): current dates use P1-P11 with P5 14:00, P7 16:20, P9 19:00, and P11 21:00, while historical dates retain the legacy table. The focused regression tests pass on main. Closing this as already resolved by #11 rather than opening a duplicate PR.