feat(dl): add absolute episode numbers filled from tvdb absolute order

Episode gains an additive absolute field services can set, an {absolute}
naming token (3-wide), and an --enrich fill from TVDB's absolute order
that never rewrites season or episode numbers.

docs/guide/downloading.md

@@ -698,6 +698,12 @@ source's values, whether or not the service already filled them in. A field the
 not answer with is left alone, and unshackle logs which fields those were, so a provider with
 a thin record cannot blank out what the service told you.
 
+`--enrich` also fills in the absolute episode number of each episode from TVDB's absolute
+order, for any series that has one and where the service did not supply it. Anime is the
+usual beneficiary, but no part of this is limited to anime. This only adds the
+[`{absolute}`](../reference/configuration/output.md#output_template) naming variable. The
+season and episode numbers are never changed.
+
 !!! warning "`--enrich` replaces the original language, which affects more than the filename"
     Track selection reads the original language, so replacing it changes which audio is
     treated as the original. That is the point when a service mislabels it, but it means a

docs/guide/output-and-naming.md

@@ -127,6 +127,7 @@ Every variable below is valid in both output and folder templates. Values are de
 | `season_episode` | Combined | `S01E05` |
 | `episode_name` | Episode title | `Pilot` |
 | `part` | Part index of a [split episode](#split-episodes), empty otherwise | `2` |
+| `absolute` | Absolute episode number, zero-padded to 3 digits, empty when unknown | `007` |
 | `date` | ISO air date for daily/dated content | `2024-06-01` |
 
 !!! note "Daily & sports content"

docs/reference/configuration/output.md

@@ -35,7 +35,7 @@ folder-kind keys.
 
 ??? example "All valid template variables"
     `title`, `year`, `season`, `episode`, `season_episode`, `episode_name`, `part`,
-    `date`, `quality`, `resolution`, `source`, `tag`, `track_number`, `artist`,
+    `absolute`, `date`, `quality`, `resolution`, `source`, `tag`, `track_number`, `artist`,
     `album_artist`, `album`, `disc`, `track_total`, `disc_total`, `release_type`, `genre`,
     `explicit`, `isrc`, `upc`, `label`, `audio`, `audio_channels`, `audio_full`, `atmos`,
     `dual`, `multi`, `dubbed`, `video`, `hdr`, `hfr`, `edition`, `repack`, `lang_tag`,
@@ -51,6 +51,14 @@ folder-kind keys.
     `{season_episode}`, and note that it is always empty in a folder template, since
     folders do not carry the part.
 
+!!! tip "`{absolute}` counts episodes across seasons"
+    `absolute` holds the absolute episode number, zero-padded to 3 digits (`007`), and is
+    empty on titles that have none. It is added to the name and never replaces `{season}`
+    or `{episode}`. Any series with a TVDB absolute order can use it, anime most often.
+    Services can supply it, and
+    [`--enrich`](../../guide/downloading.md#metadata-and-tagging) fills it in from TVDB.
+    Use `{absolute?}` so the name stays clean when it is unknown.
+
 ## Tagging & naming keys
 
 | Key | Type | Default | Description |