Stop storing raw file bytes in media.text_content

`text_content` is an extracted-text cache, but nothing stopped it from
holding a dump of bytes:

- `fileToText` ended its switch with `default: return buffer.toString("utf-8")`
  and defaulted a missing extension to "txt", so any binary was decoded.
- Both extraction callers gated on `media_type == "document"`, and
  `attachmentFileKind` classes everything non-image/audio/video as a
  document: an SVG, a zip, a spreadsheet, a .bin.
- Nothing capped the length, so a 20 MB attachment could leave 20 MB of
  text in the database.
- `storeChatAttachments` copied the text onto a second `media` row, and
  `SELECT m.*` pulled the column into page props and API responses.

On a real install an SVG held 6852 characters of markup and a
`.designcraft` file held 142 KB of raw bytes.

Changes:

- `file-to-text.ts` lists the text extensions explicitly and returns
  undefined for anything else; no extension is no text.
- `can-extract-text.ts` is the one allowlist (reusing
  `BotTextFileExtensions`), used by both upload routes and by
  `uploadAndRecordMedia`; `extension-of.ts` is shared with the storage
  catalog instead of duplicated.
- `BotAttachmentTextStoreMaxChars` (200k) caps the column via
  `cap-text-content.ts`.
- `store-chat-attachments.ts` no longer copies the text; ingestion
  re-reads the bytes once.
- `media-columns.ts` selects every media column but `text_content`, which
  now has to be asked for (`grab-messages-media`'s reply path and
  ingestion do); the media CRUD routes sanitize rows they write.
- `ingest-bot-file.ts` decides on size alone, since a cached slice made
  an oversized file look already read.
- `bun run media:prune-text` cleans rows that were already stored
  (rerunnable, with a VACUUM hint).

Verified on the dev database: both bad rows cleared (146 KB), rerun
reports nothing to do.

src/pages/api/admin/bots/upload-attachment.ts

@@ -8,6 +8,7 @@ import type { BotMessageAttachment } from "@/src/types";
 import AppError from "@/src/utils/app-error";
 import attachmentFileKind from "@/src/utils/attachment-file-kind";
 import bufferFromBase64 from "@/src/utils/buffer-from-base-64";
+import canExtractText from "@/src/utils/can-extract-text";
 import parseWithSchema from "@/src/utils/parse-with-schema";
 import isReadOnlyUser from "@/src/utils/rbac/is-read-only-user";
 import safeErrorMessage from "@/src/utils/safe-error-message";
@@ -64,7 +65,7 @@ export const handler: BunextAPIRouteHandler<
             media_mime_type: ext,
             media_paradigms: ["bot-attachment"],
             media: { title: name },
-            extract_media_text_content: media_type == "document",
+            extract_media_text_content: canExtractText({ name, mime_type: mime }),
             user: { id: Number(user.id) },
         }).catch(async (error) => {
             await logError({ title: `Attachment ${name} couldn't be saved`, error }).catch(() => {});