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/bot-files/store-chat-attachments.test.ts

@@ -0,0 +1,34 @@
+import { describe, expect, test } from "bun:test";
+
+/**
+ * The module's own source, since the regression it guards is what the code
+ * writes to the database, not what it returns.
+ */
+async function source() {
+    return await Bun.file(
+        `${import.meta.dir}/store-chat-attachments.ts`,
+    ).text();
+}
+
+describe("storeChatAttachments", () => {
+    /**
+     * The same text used to be copied onto the new `bot-file` media row,
+     * so a chat upload kept a second copy of its extracted text (and left
+     * it behind when the upload was pruned). The text belongs only on the
+     * message's own `bot-attachment` row, where a reply reads it;
+     * ingestion re-reads the bytes through `extractBotFileText`.
+     */
+    test("never writes text_content onto the file's media row", async () => {
+        const code = await source();
+
+        expect(code).not.toContain("SET text_content");
+        expect(code).not.toContain("text_content = ?");
+    });
+
+    test("still saves the bytes and queues the ingest", async () => {
+        const code = await source();
+
+        expect(code).toContain("recordBotFile(");
+        expect(code).toContain("enqueueFileIngest(");
+    });
+});