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.

docs/priority_tags_help.md

@@ -30,7 +30,8 @@ Aliases live inside `()` and are separated with `|`. The canonical name is what
 When your path template contains `{first_tag}`, the app picks a folder name based on your priority list and the model’s own tags:
 
 - It checks the priority list from top to bottom. If a canonical tag or any of its aliases appear in the model tags, that canonical name becomes the folder name.
-- If no priority tags are found but the model has tags, the very first model tag is used.
+- If no priority tags are found but the model has tags, the first tag that can be used as a folder name is chosen.
+- Tags that contain a comma, or that are longer than 50 characters, are treated as unusable and skipped: some uploaders pack their whole keyword list into a single tag. If every tag is unusable, the folder falls back to `no tags`.
 - If the model has no tags at all, the folder falls back to `no tags`.
 
 ### Example
@@ -42,6 +43,7 @@ With a template like `/{model_type}/{first_tag}` and the priority entry list `ch
 | `["chars", "female"]` | `character` | `chars` matches the `character` alias, so the canonical wins. |
 | `["anime", "portrait"]` | `style` | `anime` hits the `style` entry, so its canonical label is used. |
 | `["portrait", "bw"]` | `portrait` | No priority match, so the first model tag is used. |
+| `["lora, character, rosie, ... face"]` | `no tags` | The only tag is a keyword dump, so it is skipped. |
 | `[]` | `no tags` | Nothing to match, so the fallback is applied. |
 
 ## 3. Save the Settings
@@ -61,10 +63,12 @@ After editing the entry list, press **Enter** to save. Use **Shift+Enter** whene
 - Keep canonical names short and meaningful—they become folder names.
 - Place the most important categories first; the first match wins.
 - Avoid duplicate canonical names within the same list; only the first instance is used.
+- Folder names built from tags are sanitized for filesystem safety and truncated to 50 characters.
 
 ## Troubleshooting
 
 - **Unexpected folder name?** Check that the canonical name you want is placed before other matches.
+- **Folder named `no tags`?** Every model tag was either missing or unusable (a comma-separated keyword dump, or longer than 50 characters). Add the tags you care about to your priority list so they match by name instead.
 - **Alias not working?** Ensure the alias is inside parentheses and separated with `|`, e.g. `character(char|chars)`.
 - **Validation error?** Look for missing parentheses or stray commas. Each entry must follow the `canonical(alias|alias)` pattern or just `canonical`.