feat: add --from/--to date range filtering to events list

[junior-ricon]

Summary

• Add --from and --to flags to calendula events list for server-side date filtering
• Thread TimeRange from io-calendar through CaldavClient and Client
• Either flag can be used independently (open-ended ranges)

Depends on: pimalaya/io-calendar#1

Usage

# Events this week
calendula events list calendar --from 2026-02-14 --to 2026-02-21

# All events from today onwards
calendula events list calendar --from 2026-02-14

# All events up to a deadline
calendula events list calendar --to 2026-03-01

Changes

• src/event/command/list.rs — Parse --from/--to as NaiveDate, convert to TimeRange, call list_events_in_range() when present
• src/client.rs — Add list_events_in_range() that delegates to backend
• src/caldav/client.rs — Add list_events_in_range() using ListCalendarItems::with_time_range()
• Cargo.toml — Point io-calendar at fork (temporary, until io-calendar PR merges)

Test plan

• events list calendar without flags still works (no regression)
• events list calendar --from 2026-02-14 --to 2026-02-21 returns only events in range
• events list calendar --from 2026-02-14 returns events from that date onwards
• events list calendar --to 2026-03-01 returns events up to that date
• --help shows the new flags with descriptions

[junior-ricon]

Updated based on review feedback from two colleagues:

• Removed sentinel dates (99991231T235959Z, 19700101T000000Z) — now that io-calendar's TimeRange has Option fields, open-ended ranges are expressed cleanly.
• Updated import path to use the public re-export (io_calendar::caldav::TimeRange) instead of reaching into internal modules.
• Added warning for vdir backend — logs when date filtering flags are used with a backend that doesn't support server-side filtering.

[junior-ricon]

Final updates after three rounds of internal review:

• --to is now inclusive — --to 2026-02-21 includes events on Feb 21 (internally shifts end bound to next day)
• Explicit error on date overflow instead of silent fallback
• Extracted build_time_range into a testable function
• 6 unit tests covering inclusive semantics, month/year boundaries, and edge cases

Note: Cargo.toml still points at the io-calendar fork — needs to be reverted once pimalaya/io-calendar#1 merges.