chore(forge): move issue templates to .forgejo/, add config + PR template

The workflow split draws the line at secrets: .forgejo/ is what Codeberg
sees and contributors can trigger, .gitea/ is build infrastructure. Issue
templates were the one contributor-facing thing still living in .gitea/.
Forgejo searches .forgejo -> .gitea -> .github -> docs and stops at the
first hit, so this is a no-op on Codeberg and merely makes the convention
true; Gitea loses the templates, which is correct, as issues aren't filed
there.

Fixes a label that never applied: crash_report.md asked for priority:high,
but the label is priority/high, so every crash report has been landing
unprioritised.

The bug template now asks which channel the app came from and which
account type the affected calendar uses. Provider behaviour diverges
sharply between Google, CalDAV, local and subscribed calendars — a
disproportionate share of past bugs turned out to be one account type
only — and the two published channels can be versions apart. Time zone is
requested for date and all-day problems, which is where it has mattered
every time.

Adds an ISSUE_TEMPLATE config.yml pointing translators at Weblate before
they open an issue here, plus a PR template that asks for the linked issue
and flags the two easy mistakes: an undiscussed feature, and targeting
main instead of the milestone's release branch. Blank issues stay enabled —
the ToDo label exists for what the templates don't cover.

.gitea/ISSUE_TEMPLATE/bug_report.md

@@ -1,23 +0,0 @@
----
-name: Bug report
-about: Something doesn't work the way it should
-title: ""
-labels:
-  - bug
----
-
-### What happened
-
-
-### What you expected
-
-
-### Steps to reproduce
-1.
-2.
-3.
-
-### Environment
-- Calendula version: <!-- Settings → bottom of the screen -->
-- Android version:
-- Device:

.gitea/ISSUE_TEMPLATE/crash_report.md

@@ -1,27 +0,0 @@
----
-name: Crash report
-about: Report a crash. Calendula can capture this for you (Settings → Report a problem, or the prompt after a crash) — it copies the report to your clipboard and prefills this form.
-title: "Crash: "
-labels:
-  - bug
-  - crash
-  - priority:high
----
-
-<!--
-Thanks for reporting a crash in Calendula!
-
-If the app prefilled this for you, the crash report is already below — just add
-what you were doing and submit. Otherwise, paste the report from your clipboard
-into the code block. The report contains only app/Android/device versions and the
-stack trace — no personal data or calendar content.
--->
-
-### What happened
-
-
-### Crash report
-
-```
-(paste the crash report here)
-```

.gitea/ISSUE_TEMPLATE/feature_request.md

@@ -1,16 +0,0 @@
----
-name: Feature request
-about: Suggest an idea or improvement
-title: ""
-labels:
-  - feat
----
-
-### What would you like Calendula to do?
-
-
-### Why — what problem does it solve?
-
-
-### Anything else
-<!-- mockups, examples from other apps, alternatives you considered -->

.gitea/ISSUE_TEMPLATE/question.md

@@ -1,19 +0,0 @@
----
-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: