feat: complete field parity, harden export/import, add tests

Export/Import improvements:
- Replace pagination with direct SQL query (db_sqlite_get_all_chat)
- Wrap import in SQL transaction with rollback on error
- Add fsync before fclose in export for data safety
- Sort merged output by timestamp with secondary key (stanza_id, from_jid)
- Export archive_id and marked_read from SQLite (lossless migration)
- Add progress indication every 500 messages during write/import
- Expand dedup key body prefix from 64 to 256 chars
- Fix g_slist_append O(n²) → g_slist_prepend + g_slist_reverse O(n)

Field parity (to_jid, to_resource, marked_read):
- Add fields to ff_parsed_line_t struct
- Write/parse to:|to_res:|read: metadata tags in flatfile format
- Pass to_resource through _ff_add_message and all callers
- Add marked_read to ProfMessage struct with -1 default (unset)
- Preserve fields across export/import round-trips

Tests (19 new: 11 unit + 8 functional):
- Unit: to_jid_and_marked_read, bracket_in_stanza_id, backslash_in_resource,
  mucpm_type, all_enc_types, crlf_handling, to_jid_special_chars,
  multiple_lines, parsed_line_free_null_safe, no_space_rejected,
  unclosed_bracket
- Functional: export_idempotent_no_duplicates, export_lmc_correction_survives,
  switch_preserves_old_backend_data, export_all_contacts,
  import_double_dedup, verify_after_export,
  switch_backends_independent_messages, export_empty_contact
- Rebalance test groups: move Chat Session from Group 3 to Group 4
  (25/33/30/27 instead of 25/33/36/21)
- Remove hardcoded test counts from group comments

Man page:
- Document /history switch sqlite|flatfile

tests/functionaltests/functionaltests.c

@@ -16,9 +16,9 @@
  *
  * Tests are organized into groups for better maintainability and parallel execution:
  *   Group 1: Connect, Ping, Rooms, Software, Last Activity, Autoping
- *   Group 2: Message, Receipts, Roster, DB History (+2 with SQLite)
- *   Group 3: Chat Session, Presence, Disconnect, Disco
- *   Group 4: MUC, Carbons
+ *   Group 2: Message, Receipts, Roster, DB History (+export/import with SQLite)
+ *   Group 3: Presence, Disconnect, Disco
+ *   Group 4: Chat Session, MUC, Carbons
  *
  * Parallel execution:
  *   ./functionaltests        - run all tests sequentially
@@ -85,7 +85,6 @@ main(int argc, char* argv[])
     /* ============================================================
      * GROUP 1: Connect, Ping, Rooms, Software, Last Activity
      * Basic XMPP session establishment and server queries
-     * (19 tests)
      * ============================================================ */
     const struct CMUnitTest group1_tests[] = {
         /* Connection tests - verify login, roster, bookmarks */
@@ -131,13 +130,20 @@ main(int argc, char* argv[])
     /* ============================================================
      * GROUP 2: Message, Receipts, Roster, DB History
      * Core messaging and contact management
-     * (25 tests with SQLite, 23 without)
      * ============================================================ */
     const struct CMUnitTest group2_tests[] = {
 #ifdef HAVE_SQLITE
         /* Export/Import — cross-backend migration (SQLite ↔ flat-file) */
         PROF_FUNC_TEST(export_sqlite_to_flatfile),
         PROF_FUNC_TEST(import_flatfile_to_sqlite),
+        PROF_FUNC_TEST(export_idempotent_no_duplicates),
+        PROF_FUNC_TEST(export_lmc_correction_survives),
+        PROF_FUNC_TEST(switch_preserves_old_backend_data),
+        PROF_FUNC_TEST(export_all_contacts),
+        PROF_FUNC_TEST(import_double_dedup),
+        PROF_FUNC_TEST(verify_after_export),
+        PROF_FUNC_TEST(switch_backends_independent_messages),
+        PROF_FUNC_TEST(export_empty_contact),
 #endif
 
         /* Basic message send/receive */
@@ -173,19 +179,10 @@ main(int argc, char* argv[])
     };
 
     /* ============================================================
-     * GROUP 3: Chat Session, Presence, Disconnect
-     * Session routing, status management, clean teardown
-     * (22 tests)
+     * GROUP 3: Presence, Disconnect, Disco
+     * Status management, clean teardown, service discovery
      * ============================================================ */
     const struct CMUnitTest group3_tests[] = {
-        /* Chat session management - bare/full JID routing */
-        PROF_FUNC_TEST(sends_message_to_barejid_when_contact_offline),
-        PROF_FUNC_TEST(sends_message_to_barejid_when_contact_online),
-        PROF_FUNC_TEST(sends_message_to_fulljid_when_received_from_fulljid),
-        PROF_FUNC_TEST(sends_subsequent_messages_to_fulljid),
-        PROF_FUNC_TEST(resets_to_barejid_after_presence_received),
-        PROF_FUNC_TEST(new_session_when_message_received_from_different_fulljid),
-
         /* Presence - online/away/xa/dnd/chat status management */
         PROF_FUNC_TEST(presence_online),
         PROF_FUNC_TEST(presence_online_with_message),
@@ -224,11 +221,18 @@ main(int argc, char* argv[])
     };
 
     /* ============================================================
-     * GROUP 4: MUC, Carbons
-     * Multi-user chat and message synchronization
-     * (21 tests)
+     * GROUP 4: Chat Session, MUC, Carbons
+     * Session routing, multi-user chat, message synchronization
      * ============================================================ */
     const struct CMUnitTest group4_tests[] = {
+        /* Chat session management - bare/full JID routing */
+        PROF_FUNC_TEST(sends_message_to_barejid_when_contact_offline),
+        PROF_FUNC_TEST(sends_message_to_barejid_when_contact_online),
+        PROF_FUNC_TEST(sends_message_to_fulljid_when_received_from_fulljid),
+        PROF_FUNC_TEST(sends_subsequent_messages_to_fulljid),
+        PROF_FUNC_TEST(resets_to_barejid_after_presence_received),
+        PROF_FUNC_TEST(new_session_when_message_received_from_different_fulljid),
+
         /* MUC room join with various options - XEP-0045 */
         PROF_FUNC_TEST(sends_room_join),
         PROF_FUNC_TEST(sends_room_join_with_nick),
@@ -271,8 +275,8 @@ main(int argc, char* argv[])
     } groups[] = {
         { "Group 1: Connect/Ping/Rooms/Software/LastActivity/Autoping", group1_tests, ARRAY_SIZE(group1_tests) },
         { "Group 2: Message/Receipts/Roster/DBHistory", group2_tests, ARRAY_SIZE(group2_tests) },
-        { "Group 3: Session/Presence/Disconnect/Disco", group3_tests, ARRAY_SIZE(group3_tests) },
-        { "Group 4: MUC/Carbons", group4_tests, ARRAY_SIZE(group4_tests) },
+        { "Group 3: Presence/Disconnect/Disco", group3_tests, ARRAY_SIZE(group3_tests) },
+        { "Group 4: Session/MUC/Carbons", group4_tests, ARRAY_SIZE(group4_tests) },
     };
     const int num_groups = ARRAY_SIZE(groups);