refactor: address PR #105 review feedback

Apply fixes, refactors and test additions requested by reviewer on PR #105.

Fixes:
- database: warn and notify user on duplicate archive_id instead of
  silently debug-logging it (R05).
- database: add missing '[' in "[DB Migration]" log prefix (R06).
- xmpp/resource: NULL-out name/status after g_free to avoid double-free
  via roster_list.c cleanup path (R09, R23).
- common: widen strtoi_range internal storage from int to long so that
  values in (INT_MAX, LONG_MAX] are rejected as out-of-range instead of
  being silently truncated on 64-bit platforms (R25).

Refactors:
- xmpp/message: extract _receive_omemo helper, removing three copies of
  the OMEMO receive block in groupchat / MUC-PM / chat handlers (R04).
- omemo: flatten deeply nested device-list processing via guard-clause
  continues (R11).
- tools/autocomplete: merge two nested ifs into a single && condition
  (R13).
- ui/titlebar: extract _show_trust_indicator and inline _wprintw_withattr
  wrapper, collapsing three near-identical trust-indicator blocks (R22).
- config/tlscerts: drop _checked_g_strdup wrapper; g_strdup is
  NULL-safe per glib documentation (R19).
- ui/inputwin: use auto_gchar for spellcheck word instead of manual
  g_free (R20).
- tools/editor: drop outdated "Deprecated synchronous" comment that
  no longer matches the callback-based implementation (R28).

Tests:
- tests/command/cmd_ac: rename segfaults_when_empty ->
  no_segfault_when_empty; expand cycling coverage to three files plus
  backward SHIFT-TAB traversal (R16, R17).
- tests/common: add strtoi_range overflow/underflow and strtol-parsing
  consistency tests (R25).
- tests/xmpp/jid: add test for '@' inside resourcepart per RFC 6122
  section 2.4 (R26).

Misc:
- xmpp/omemo: change omemo_error_to_string return type from char* to
  gchar* for glib consistency (R01).
- subprojects/libstrophe: point wrap-git at our fork at
  git.jabber.space/devs/libstrophe-gh (R24).
- RELEASE_GUIDE: drop "Updating website" section referring to an
  upstream site that is not ours (R18).

tests/unittests/test_common.c

@@ -9,6 +9,8 @@
 #include "xmpp/resource.h"
 #include "common.h"
 #include "prof_cmocka.h"
+#include <limits.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include "tests/unittests/ui/stub_ui.h" // Include for mocking cons_show
 
@@ -519,6 +521,63 @@ strtoi_range__returns__correct_values_when_err_msg_null(void** state)
     assert_false(result);
 }
 
+void
+strtoi_range__returns__false_for_integer_overflow_underflow(void** state)
+{
+    int value;
+    gchar* err_msg = NULL;
+    gboolean result;
+    char buf[64];
+
+    // INT_MAX + 1 overflows
+    snprintf(buf, sizeof(buf), "%lld", (long long)INT_MAX + 1);
+    result = strtoi_range(buf, &value, INT_MIN, INT_MAX, &err_msg);
+    assert_false(result);
+    g_free(err_msg);
+    err_msg = NULL;
+
+    // INT_MIN - 1 underflows
+    snprintf(buf, sizeof(buf), "%lld", (long long)INT_MIN - 1);
+    result = strtoi_range(buf, &value, INT_MIN, INT_MAX, &err_msg);
+    assert_false(result);
+    g_free(err_msg);
+    err_msg = NULL;
+
+    // Extreme overflow, larger than `long`
+    result = strtoi_range("9999999999999999999999999999999999", &value, INT_MIN, INT_MAX, &err_msg);
+    assert_false(result);
+    g_free(err_msg);
+    err_msg = NULL;
+}
+
+void
+strtoi_range__returns_consistent_with_strtol_parsing(void** state)
+{
+    int value;
+    gchar* err_msg = NULL;
+    gboolean result;
+
+    // Hexadecimal: "0x10" -> 16
+    result = strtoi_range("0x10", &value, 0, 100, &err_msg);
+    assert_true(result);
+    assert_int_equal(16, value);
+    g_free(err_msg);
+    err_msg = NULL;
+
+    // Octal: "010" -> 8
+    result = strtoi_range("010", &value, 0, 100, &err_msg);
+    assert_true(result);
+    assert_int_equal(8, value);
+    g_free(err_msg);
+    err_msg = NULL;
+
+    // Floating point "0.8" should fail: '.' is not a valid integer char
+    result = strtoi_range("0.8", &value, -10, 10, &err_msg);
+    assert_false(result);
+    g_free(err_msg);
+    err_msg = NULL;
+}
+
 void
 string_to_verbosity__returns__correct_values(void** state)
 {