fix: OTR/presence/OMEMO correctness, stanza-id disco gate, build hardening

- OTR: strip the whitespace tag by shifting the full message tail incl. the NUL, not tag_length bytes, so the body is no longer duplicated for messages longer than the tag.
- presence: snapshot the resource fields before connection_add_available_resource() takes ownership, removing a use-after-free in the own-presence path.
- OMEMO: propagate _omemo_finalize_identity_load() failure on connect (log + cons_show_error + stop) instead of leaving OMEMO silently unavailable.
- OMEMO: guard NULL fingerprint decode in _omemo_fingerprint_decode / omemo_is_trusted_identity / omemo_trust and log every decode failure instead of failing silently.
- stanza-id: gate XEP-0359 dedup on disco urn:xmpp:sid:0 (the `by` JID or its domain), falling back to no-dedup when caps are unknown; add functional tests for trusted vs untrusted server.
- accounts: narrow the group-name sanitizer to the characters GKeyFile forbids in headers ([ ] \n \r), keeping `=` and `#`, so read/write stays symmetric.
- build: re-introduce compiler/sanitizer flags in a Pikaur-safe form (opt-in sanitizers, -Wsign-compare) and fix the resulting -Wsign-compare warnings (incl. proftest _mkdir_recursive).fix: OTR/presence/OMEMO correctness, stanza-id disco gate, build hardening

Author: jabber.developer2 <jabber.developer2@jabber.space>

tests/functionaltests/proftest.c

@@ -119,10 +119,9 @@ _create_dir(const char* name)
 gboolean
 _mkdir_recursive(const char* dir)
 {
-    int i;
     gboolean result = TRUE;
 
-    for (i = 1; i <= strlen(dir); i++) {
+    for (size_t i = 1; i <= strlen(dir); i++) {
         if (dir[i] == '/' || dir[i] == '\0') {
             gchar* next_dir = g_strndup(dir, i);
             result = _create_dir(next_dir);