fix(widget): drive agenda range via reactive Glance state

The agenda widget loaded and sliced its data in the provideGlance preamble
and captured it as a non-reactive local. updateAll() reliably recomposes a
live Glance session but does not reliably re-run that preamble, so a range
change was redrawn against the stale slice (intermittently — only when no
session was alive did it pick up the new range). This is the same platform
limitation the month widget already works around.

Mirror that pattern: load the widest selectable window once, store the range
in per-instance Glance state (AGENDA_RANGE_KEY), read it reactively via
currentState, and slice in the composition. The settings setter writes the
state into each instance and recomposes, so a range change now reflects via
plain recomposition regardless of session lifecycle.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/ISSUE_TEMPLATE/question.md

@@ -0,0 +1,19 @@
+---
+name: Question
+about: Ask how something works or get help using Calendula
+title: ""
+labels:
+  - question
+---
+
+### Your question
+
+
+### What you've tried
+<!-- so far, if anything -->
+
+
+### Context
+- Calendula version: <!-- Settings → bottom of the screen -->
+- Android version:
+- Device: