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>

src/common.c

@@ -294,7 +294,7 @@ str_replace(const char* string, const char* substr,
     wr = newstr;
 
     while ((tok = strstr(head, substr))) {
-        size_t l = tok - head;
+        size_t l = g_diff_to_gsize(tok, head);
         memcpy(wr, head, l);
         wr += l;
         memcpy(wr, replacement, len_replacement);
@@ -309,6 +309,16 @@ str_replace(const char* string, const char* substr,
     return newstr;
 }
 
+gsize
+g_diff_to_gsize(const void* end, const void* start)
+{
+    if (end < start) {
+        log_error("g_diff_to_gsize: end < start (%p < %p)", end, start);
+        return 0;
+    }
+    return (gsize)((const char*)end - (const char*)start);
+}
+
 gboolean
 strtoi_range(const char* str, int* saveptr, int min, int max, gchar** err_msg)
 {
@@ -359,9 +369,9 @@ string_matches_one_of(const char* what, const char* is, gboolean is_can_be_null,
         char errmsg[256] = { 0 };
         size_t sz = 0;
         int s = snprintf(errmsg, sizeof(errmsg) - sz, "%s must be one of:", what);
-        if (s < 0 || s + sz >= sizeof(errmsg))
+        if (s < 0 || (size_t)s + sz >= sizeof(errmsg))
             return ret;
-        sz += s;
+        sz += (size_t)s;
 
         cur = first;
         va_start(ap, first);
@@ -375,12 +385,12 @@ string_matches_one_of(const char* what, const char* is, gboolean is_can_be_null,
                 errmsg[sz] = '\0';
                 s = snprintf(errmsg + sz, sizeof(errmsg) - sz, " or '%s'.", cur);
             }
-            if (s < 0 || s + sz >= sizeof(errmsg)) {
+            if (s < 0 || (size_t)s + sz >= sizeof(errmsg)) {
                 log_debug("Error message too long or some other error occurred (%d).", s);
                 s = -1;
                 break;
             }
-            sz += s;
+            sz += (size_t)s;
             cur = next;
         }
         va_end(ap);
@@ -431,7 +441,7 @@ str_xml_sanitize(const char* const str)
         return NULL;
     }
 
-    GString* sanitized = g_string_new_len(NULL, strlen(str));
+    GString* sanitized = g_string_new_len(NULL, (gssize)strlen(str));
     const char* curr = str;
 
     while (*curr != '\0') {
@@ -690,7 +700,7 @@ get_file_paths_recursive(const char* path, GSList** contents)
 }
 
 gchar*
-get_random_string(int length)
+get_random_string(size_t length)
 {
     GRand* prng;
     gchar* rand;
@@ -701,7 +711,7 @@ get_random_string(int length)
 
     prng = g_rand_new();
 
-    for (int i = 0; i < length; i++) {
+    for (size_t i = 0; i < length; i++) {
         rand[i] = alphabet[g_rand_int_range(prng, 0, endrange)];
     }
     g_rand_free(prng);