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- tools/editor: drop outdated "Deprecated synchronous" comment that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

@@ -237,24 +237,16 @@ _name_to_tlscert_name_(const char* in, tls_cert_name_t* out, const char* name)
     }
 }
 
-static gchar*
-_checked_g_strdup(const char* in)
-{
-    if (in == NULL)
-        return NULL;
-    return g_strdup(in);
-}
-
 TLSCertificate*
 tlscerts_new(const char* fingerprint_sha1, int version, const char* serialnumber, const char* subjectname,
              const char* issuername, const char* notbefore, const char* notafter,
              const char* key_alg, const char* signature_alg, const char* pem,
              const char* fingerprint_sha256, const char* pubkey_fingerprint)
 {
-    return _tlscerts_new(_checked_g_strdup(fingerprint_sha1), version, _checked_g_strdup(serialnumber), _checked_g_strdup(subjectname),
-                         _checked_g_strdup(issuername), _checked_g_strdup(notbefore), _checked_g_strdup(notafter),
-                         _checked_g_strdup(key_alg), _checked_g_strdup(signature_alg), _checked_g_strdup(pem),
-                         _checked_g_strdup(fingerprint_sha256), _checked_g_strdup(pubkey_fingerprint));
+    return _tlscerts_new(g_strdup(fingerprint_sha1), version, g_strdup(serialnumber), g_strdup(subjectname),
+                         g_strdup(issuername), g_strdup(notbefore), g_strdup(notafter),
+                         g_strdup(key_alg), g_strdup(signature_alg), g_strdup(pem),
+                         g_strdup(fingerprint_sha256), g_strdup(pubkey_fingerprint));
 }
 
 static void