fix(organize): stop keyword-dump tags from becoming folder names (#1119)

CivitAI tags are normally short single-concept labels, but some uploaders
pack their entire keyword list into one tag. The model in #1119 carries
"lora, character, rosie, irish, ... face" as a single 181-character tag.
Priority resolution matches aliases by exact equality, so that tag matched
nothing and resolve_priority_tag_for_model fell back to tags[0] -- the blob.
With the default "{base_model}/{first_tag}" template the model was filed
under "Krea 2/<181-character blob>/", and the full path plus the
".civitai.info" sidecar and the preview images next to it ran into the
Windows MAX_PATH limit.

Tags also bypassed sanitization on the way into a path: both
calculate_relative_path_for_model and DownloadManager._calculate_relative_path
sanitized model_name and version_name but interpolated {first_tag} verbatim,
so a tag containing "/" or ":" silently produced nested or illegal folders.

Two changes:

- The fallback skips tags that cannot serve as a folder name.
  is_usable_path_tag rejects comma-separated keyword dumps and tags longer
  than MAX_PATH_TAG_LENGTH; the resolver returns "" when nothing usable is
  left, which callers already render as "no tags". Whole-tag priority
  matching is untouched, so existing priority configurations behave the
  same.
- sanitize_folder_name gains an optional max_length, and every tag-derived
  segment now goes through it. Tags are capped at MAX_PATH_TAG_LENGTH, model
  and version names at MAX_FOLDER_NAME_LENGTH, and rendered filename stems at
  MAX_FILENAME_STEM_LENGTH.

For the reported model the folder becomes "Krea 2/base model" instead of the
blob, and the full path drops from 235 to 64 characters.

Existing libraries are not migrated up front: a path is only recomputed on
download, on an auto-organize run or when a filename template is applied, and
values already inside the caps are left byte-identical. Models previously
filed under a keyword-dump folder move on the next auto-organize run.

py/utils/constants.py

@@ -293,6 +293,19 @@ DEFAULT_DOWNLOAD_PATH_TEMPLATES: Dict[str, str] = {
     "other": "",
 }
 
+# Length guards for template placeholders that end up in file and folder names.
+# Windows enforces MAX_PATH (260 characters) on the full path and 255 on a
+# single path component, and a model folder also has to leave room for the
+# model file, its ".civitai.info"/".json" sidecars and preview images. Values
+# stay well below those limits so the surrounding files still fit.
+#
+# Tags get a much tighter budget than other names: some CivitAI uploaders dump
+# their whole keyword list into a single tag (see issue #1119), and such a tag
+# is only useful as a folder name after truncation.
+MAX_FOLDER_NAME_LENGTH = 100
+MAX_PATH_TAG_LENGTH = 50
+MAX_FILENAME_STEM_LENGTH = 150
+
 # baseModel values from CivitAI that should be treated as diffusion models (unet)
 # These model types are incorrectly labeled as "checkpoint" by CivitAI but are actually diffusion models
 DIFFUSION_MODEL_BASE_MODELS = frozenset(