refactor(platforms): drop migration 0088 — no deviantart rows exist (#3069)

Operator confirms the instance has never used DeviantArt, so there is
nothing for 0088 to quiesce. The migration only ever had two jobs —
disable leftover `source` rows and delete a stale `credential` row — and
both were guards against data that does not exist here.

Removing it rather than keeping a no-op: a migration that runs on every
deploy to touch zero rows is a permanent cost paid for a hypothetical,
and it would read to a future reader as evidence that DeviantArt sources
once existed. `platform` has no CHECK constraint, so retiring the key
needs no schema change of its own.

alembic head returns to 0087.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

alembic/versions/0088_retire_deviantart.py

@@ -1,70 +0,0 @@
-"""retire deviantart (#3069) — quiesce the rows the dropped platform leaves behind
-
-`deviantart` is no longer a registered platform, so nothing can create or edit a
-source with that key any more. Existing rows are a different question, and the
-two tables want opposite treatment:
-
-* `source` rows are DISABLED, not deleted. The row is the only place the
-  artist's DeviantArt URL is recorded, and losing it is unrecoverable — whereas
-  a disabled row is visible in the UI and reversible by hand. Disabling is also
-  required for correctness, not just tidiness: with the platform unregistered
-  the download path falls through to gallery-dl, which carries its OWN built-in
-  deviantart extractor, so an enabled row would have gone on downloading from a
-  platform the product dropped.
-
-* the `credential` row IS deleted. It is an encrypted DeviantArt session cookie
-  for a site FC will never call again — keeping a live credential we have no
-  use for is strictly worse than dropping it, and re-exporting from the browser
-  is the recovery path if that judgment is ever wrong.
-
-A no-op on an instance that never had a DeviantArt source, which is the
-expected case.
-
-Revision ID: 0088
-Revises: 0087
-Create Date: 2026-08-27
-"""
-from typing import Sequence, Union
-
-import sqlalchemy as sa
-from alembic import op
-
-revision: str = "0088"
-down_revision: Union[str, None] = "0087"
-branch_labels: Union[str, Sequence[str], None] = None
-depends_on: Union[str, Sequence[str], None] = None
-
-_RETIRED = "deviantart"
-
-# Written into last_error so the disabled row explains itself in the UI rather
-# than looking like an unexplained toggle someone flipped.
-_REASON = (
-    "Platform retired: FabledCurator no longer supports DeviantArt "
-    "(dropped 2026-08-27, #3069). This source was disabled automatically; "
-    "the URL is kept for reference and the row can be deleted by hand."
-)
-
-
-def upgrade() -> None:
-    conn = op.get_bind()
-    disabled = conn.execute(
-        sa.text(
-            "UPDATE source SET enabled = false, last_error = :reason "
-            "WHERE platform = :p AND enabled = true"
-        ),
-        {"reason": _REASON, "p": _RETIRED},
-    ).rowcount
-    creds = conn.execute(
-        sa.text("DELETE FROM credential WHERE platform = :p"), {"p": _RETIRED}
-    ).rowcount
-    print(f"0088: disabled {disabled} deviantart source(s), removed {creds} credential(s)")
-
-
-def downgrade() -> None:
-    # Re-enabling is deliberately NOT done: the platform is gone from the
-    # registry, so a re-enabled source would still have no backend to run on.
-    # Clearing the stamped reason is the only half that means anything.
-    op.get_bind().execute(
-        sa.text("UPDATE source SET last_error = NULL WHERE platform = :p AND last_error = :reason"),
-        {"p": _RETIRED, "reason": _REASON},
-    )