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- tools/editor: drop outdated "Deprecated synchronous" comment that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).

src/common.c

@@ -313,25 +313,25 @@ gboolean
 strtoi_range(const char* str, int* saveptr, int min, int max, gchar** err_msg)
 {
     char* ptr;
-    int val;
+    long lval;
     if (str == NULL) {
         if (err_msg)
             *err_msg = g_strdup_printf("'str' input pointer can not be NULL");
         return FALSE;
     }
     errno = 0;
-    val = (int)strtol(str, &ptr, 0);
+    lval = strtol(str, &ptr, 0);
     if (errno != 0 || *str == '\0' || *ptr != '\0') {
         if (err_msg)
             *err_msg = g_strdup_printf("Could not convert \"%s\" to a number.", str);
         return FALSE;
-    } else if (val < min || val > max) {
+    } else if (lval < (long)min || lval > (long)max) {
         if (err_msg)
             *err_msg = g_strdup_printf("Value %s out of range. Must be in %d..%d.", str, min, max);
         return FALSE;
     }
 
-    *saveptr = val;
+    *saveptr = (int)lval;
 
     return TRUE;
 }