vfs: major overhaul — device nodes, stream I/O, mode simplification

- 5-phase VFS architecture overhaul (path resolution, dir cache, watch/notify,
  symlinks, async API)
- Add character/block device node layer with /dev/null and /dev/zero built-ins
- RegisterDevice() API for custom device nodes with read/write/size callbacks
- Merge TOpenMode + TWriteMode into single TOpenMode enum
  (omRead, omWrite, omCreate, omReadWrite, omStream)
- Add stream write support: WriteFile/WriteFileAsync now accept omStream handles
  with auto-advancing offset for both device and volume FDs
- Add PPWriteOffsetHook type and writeOffsetCallback field to TFilesystem
- Add PPReadOffsetHook-based streaming reads for FAT32 and ISO9660
- Update all callers (notepad, edit, inio, wasm runner, filepicker, filedispatch,
  vterminal, stdio) to new 2-param OpenFile API
- 77 unit tests (0 failures) covering path ops, dir cache, symlinks, watch,
  device nodes, and stream read/write
- Add doc/vfs.md — comprehensive public VFS API documentation

src/driver/storage/fs/driver.storage.fs.flatfs.pas

@@ -827,6 +827,10 @@ begin
                 dirEntry^.entryType := TDirectory_Entry_Type.directoryEntry
             else
                 dirEntry^.entryType := TDirectory_Entry_Type.fileEntry;
+            dirEntry^.fileSize     := fileEntrys[i].size;
+            dirEntry^.modifiedDate := 0;
+            dirEntry^.modifiedTime := 0;
+            dirEntry^.attributes   := fileEntrys[i].attribues;
         end;
 
         kfree(void(compString));

src/driver/storage/fs/driver.storage.fs.iso9660.pas

@@ -562,6 +562,19 @@ begin
         else
             dirEntry^.entryType := TDirectory_Entry_Type.fileEntry;
 
+        dirEntry^.fileSize     := rec^.dataLen_LSB;
+        dirEntry^.attributes   := rec^.fileFlags;
+        { Convert ISO 9660 date (year-1900,month,day,hour,min,sec) to FAT-style }
+        if rec^.recDate[0] >= 80 then
+            dirEntry^.modifiedDate := (uint16(rec^.recDate[0] - 80) shl 9)
+                                   or (uint16(rec^.recDate[1]) shl 5)
+                                   or  uint16(rec^.recDate[2])
+        else
+            dirEntry^.modifiedDate := 0;
+        dirEntry^.modifiedTime := (uint16(rec^.recDate[3]) shl 11)
+                               or (uint16(rec^.recDate[4]) shl 5)
+                               or (uint16(rec^.recDate[5]) shr 1);
+
         offset := offset + rec^.recLen;
     end;
 
@@ -722,6 +735,7 @@ begin
     filesystem.createDirCallback := nil;
     filesystem.deleteFileCallback := nil;
     filesystem.deleteDirCallback := nil;
+    filesystem.renameFileCallback := nil;
     filesystem.readAsyncCallback    := nil;
     filesystem.readDirAsyncCallback := nil;