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/functions/backend/db/media/media-columns.ts

@@ -0,0 +1,40 @@
+/**
+ * The `media` columns a normal read takes, with a table alias.
+ *
+ * `text_content` is deliberately left out: it holds up to
+ * `AppData.BotAttachmentTextStoreMaxChars` of extracted document text, and
+ * every caller that only needs a file's name, type or path (`SELECT m.*`
+ * did) pulled it into memory, into page props and into API responses.
+ * Read it explicitly where it is really used:
+ * `src/bots-queue/load-attachment-parts.ts` and
+ * `src/functions/backend/db/bot-files/ingest-bot-file.ts`.
+ */
+export default function mediaColumns({
+    alias = "m",
+    with_text_content,
+}: { alias?: string; with_text_content?: boolean } = {}) {
+    const columns = [
+        "id",
+        "created_at",
+        "updated_at",
+        "user_id",
+        "title",
+        "description",
+        "summary",
+        "media_type",
+        "media_write_path",
+        "media_thumbnail_write_path",
+        "mime_type",
+        "is_primary",
+        "is_rag_ingested",
+        "archived",
+    ];
+
+    /**
+     * Only the two paths that really use it ask for it: the reply that
+     * hands a document to a model, and ingestion.
+     */
+    if (with_text_content) columns.push("text_content");
+
+    return columns.map((column) => `${alias}.${column}`).join(", ");
+}