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- tools/editor: drop outdated "Deprecated synchronous" comment that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

@@ -581,7 +581,8 @@ _add_to_db(ProfMessage* message, const char* type, const Jid* const from_jid, co
     if (rc == SQLITE_ROW) {
         log_debug("Successfully inserted message into database.");
     } else if (rc == SQLITE_DONE) {
-        log_debug("Message already exists in database (archive_id: %s), skipping.", message->stanzaid);
+        log_warning("Message already exists in database (archive_id: %s), skipping.", message->stanzaid);
+        cons_show_error("Duplicate message detected (archive_id: %s), skipping.", message->stanzaid);
     } else {
         log_error("SQLite error in _add_to_db() (step): %s", sqlite3_errmsg(g_chatlog_database));
     }
@@ -758,7 +759,7 @@ _migrate_to_v3(void)
 
 cleanup:
     if (SQLITE_OK != sqlite3_exec(g_chatlog_database, "ROLLBACK;", NULL, 0, &err_msg)) {
-        log_error("DB Migration] Unable to ROLLBACK: %s", err_msg);
+        log_error("[DB Migration] Unable to ROLLBACK: %s", err_msg);
         if (err_msg) {
             sqlite3_free(err_msg);
         }