feat: file blocks (#10)

Phase 3, part 2 (`docs/design.md`, "Next"): file blocks. Moderators block a file network-wide by its sha256, so a removed product can't come back under another name or catalog.

**Blocking**
- A file's page (Console → Blocks → a file) shows whether it's blocked and the products using it, so a moderator sees what a block removes before confirming ("Block and remove 2 products").
- Moderators reach it from a product's files (each has a Block link for them) or by pasting a sha256 into the Blocks tab, which also lists blocked files.
- Blocking a file:
  - removes every product with a revision using it. Each removal is audited as `product.remove` with the file, so creators are notified and can appeal it as before.
  - puts a `{type: "block", sha256}` change in the changes feed of every catalog hosting it, meaning: delete it whatever uses it. (t5de-catalog doesn't read the feed yet.)
  - refuses uploads with it from then on (409 `blocked`). Each attempt is audited as `file.blocked_upload` with the person and catalog, so moderators see who tried.
- Unblocking lets the file in again. The products it removed stay removed until a moderator restores them, one by one.
- Who: `product:remove` hub-wide (moderators and admins). The Blocks tab shows only for them.

**API**: `GET /api/v1/blocks`, and `GET`/`PUT`/`DELETE /api/v1/blocks/:sha256` (`docs/products.md`).

**Migration** `0013_file_blocks`: the `file_block` table, and a GIN index on revisions' file lists, so finding the products using a file doesn't scan every revision.

**Checks**
- 53 API tests pass. The new `blocks.test.ts` covers:
  - who may block
  - the preview of what a block removes
  - removal of every product using the file, across catalogs and creators
  - the changes feed, notifications and appeals
  - refused uploads and their audit entry
  - unblocking, and restoring a removed product afterwards
- Type checks pass.
- On a local hub, through the website's own forms:
  - the Block link on a product's files, for moderators only
  - the Blocks tab, for moderators only (404 for the creator)
  - the file's page, then blocking: the product is gone, its creator notified and offered Appeal
  - a re-upload through the catalog API: refused, and audited
  - unblocking, then Restore
  - Fixed along the way: an empty reason gave a generic "Some of that isn't right"; it now says "Give a reason."

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Phase 3, part 2 (`docs/design.md`, "Next"): file blocks. Moderators block a file network-wide by its sha256, so a removed product can't come back under another name or catalog.

**Blocking**
- A file's page (Console → Blocks → a file) shows whether it's blocked and the products using it, so a moderator sees what a block removes before confirming ("Block and remove 2 products").
- Moderators reach it from a product's files (each has a Block link for them) or by pasting a sha256 into the Blocks tab, which also lists blocked files.
- Blocking a file:
  - removes every product with a revision using it. Each removal is audited as `product.remove` with the file, so creators are notified and can appeal it as before.
  - puts a `{type: "block", sha256}` change in the changes feed of every catalog hosting it, meaning: delete it whatever uses it. (t5de-catalog doesn't read the feed yet.)
  - refuses uploads with it from then on (409 `blocked`). Each attempt is audited as `file.blocked_upload` with the person and catalog, so moderators see who tried.
- Unblocking lets the file in again. The products it removed stay removed until a moderator restores them, one by one.
- Who: `product:remove` hub-wide (moderators and admins). The Blocks tab shows only for them.

**API**: `GET /api/v1/blocks`, and `GET`/`PUT`/`DELETE /api/v1/blocks/:sha256` (`docs/products.md`).

**Migration** `0013_file_blocks`: the `file_block` table, and a GIN index on revisions' file lists, so finding the products using a file doesn't scan every revision.

**Checks**
- 53 API tests pass. The new `blocks.test.ts` covers:
  - who may block
  - the preview of what a block removes
  - removal of every product using the file, across catalogs and creators
  - the changes feed, notifications and appeals
  - refused uploads and their audit entry
  - unblocking, and restoring a removed product afterwards
- Type checks pass.
- On a local hub, through the website's own forms:
  - the Block link on a product's files, for moderators only
  - the Blocks tab, for moderators only (404 for the creator)
  - the file's page, then blocking: the product is gone, its creator notified and offered Appeal
  - a re-upload through the catalog API: refused, and audited
  - unblocking, then Restore
  - Fixed along the way: an empty reason gave a generic "Some of that isn't right"; it now says "Give a reason."

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: dhkatz <[email protected]>

docs/console.md

@@ -93,6 +93,8 @@ Sections (each shown only to those with something in it):
 - **Rooms**: their hosted rooms.
 - **Cases**: reports, appeals and reviews about what they control.
 - **People**: moderators and admins.
+- **Blocks**: those who remove products hub-wide (`product:remove`): blocked files, a file's page (the products using it;
+  block, unblock). Each file in a product's revisions links to its page for them.
 - **Audit**: scoped (below).
 - **Settings**: admins (registration, announcements, roles).