feat(crash): privacy-respecting crash reporting via Gitea issue

Capture uncaught exceptions on-device and let the user submit them, by
hand, as a Gitea issue — no network access, no auto-upload (the app holds
no INTERNET permission). Closes prod-readiness item 10; the issue
templates also close item 7.

- CrashReporter: uncaught-exception handler installed first in
  CalendulaApp.onCreate so startup crashes are caught too. Persists an
  allowlist-only report (app/Android/device version, locale, time, stack
  trace — nothing else) to filesDir/crash, then chains to the previous
  handler so the process still dies normally. Crash-loop detection +
  markHealthy reset.
- buildCrashReport is pure/testable; CrashReportBuilderTest asserts the
  header is exactly the allowlisted lines (guards against PII creep).
- Surfacing: next-launch dialog showing the full report verbatim (the
  privacy backstop) with a dismissed-marker so it doesn't nag; a Settings
  "Report a problem" row; and a minimal standalone CrashReportActivity
  that MainActivity routes to on a startup crash-loop, kept clear of the
  Hilt graph / DataStore theme.
- submitCrashReport copies the report to the clipboard and opens the
  prefilled Gitea issues/new URL (long traces fall back to paste).
- .gitea/ISSUE_TEMPLATE: crash_report, bug_report, feature_request.

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

app/src/test/java/de/jeanlucmakiola/calendula/data/crash/CrashReportBuilderTest.kt

@@ -0,0 +1,56 @@
+package de.jeanlucmakiola.calendula.data.crash
+
+import com.google.common.truth.Truth.assertThat
+import org.junit.jupiter.api.Test
+
+class CrashReportBuilderTest {
+
+    private val context = CrashContext(
+        appVersionName = "2.7.0",
+        appVersionCode = 20700,
+        sdkInt = 34,
+        androidRelease = "14",
+        manufacturer = "Google",
+        model = "Pixel 7",
+        locale = "en-DE",
+    )
+
+    @Test
+    fun `report carries the allowlisted facts and the stack trace`() {
+        val report = buildCrashReport(context, IllegalStateException("boom"), nowMillis = 0L)
+
+        assertThat(report).startsWith("Calendula crash report")
+        assertThat(report).contains("App version: 2.7.0 (20700)")
+        assertThat(report).contains("Android: 14 (API 34)")
+        assertThat(report).contains("Device: Google Pixel 7")
+        assertThat(report).contains("Locale: en-DE")
+        // The exception type + message and a frame from this test are present.
+        assertThat(report).contains("IllegalStateException")
+        assertThat(report).contains("boom")
+        assertThat(report).contains("CrashReportBuilderTest")
+    }
+
+    @Test
+    fun `nested causes are included`() {
+        val cause = NullPointerException("inner")
+        val report = buildCrashReport(context, RuntimeException("outer", cause), nowMillis = 0L)
+
+        assertThat(report).contains("outer")
+        assertThat(report).contains("Caused by")
+        assertThat(report).contains("inner")
+    }
+
+    @Test
+    fun `report holds only the allowlisted lines before the stack trace`() {
+        val report = buildCrashReport(context, Exception("x"), nowMillis = 0L)
+        val header = report.substringBefore("Stack trace:").trim().lines()
+
+        // No identifiers, accounts, or extra fields ever creep into the header:
+        // it is exactly the six allowlisted lines plus the title.
+        assertThat(header).hasSize(6)
+        assertThat(header.first()).isEqualTo("Calendula crash report")
+        assertThat(header.map { it.substringBefore(":") }).containsExactly(
+            "Calendula crash report", "App version", "Android", "Device", "Locale", "Time",
+        ).inOrder()
+    }
+}