docs: add block/mute user relations, emoji-sync CLI, and uid indexes

- Add `/block`, `/mute` endpoints with block/unblock and mute/unmute functionality in `routers/relations.py`, hiding blocked users' content everywhere except their own profile while muting only suppresses notifications
- Introduce `devplace emoji-sync` CLI command to regenerate `static/js/emoji-shortcodes.js` from the emoji library, documented in `CLAUDE.md` and wired in `cli.py`
- Create `get_blocked_uids()` database helper and apply it in `content.py` `load_detail()` to filter blocked users' posts from detail views
- Implement `_uid_index()` and `_drop_index()` helpers in `database.py` for unique uid indexes across tables, with `user_relations` added to `SOFT_DELETE_TABLES`
- Document new routes in `AGENTS.md` and `README.md`, including emoji shortcodes rendering behavior distinct from the emoji picker

devplacepy/static/js/components/AppLightbox.js

@@ -32,6 +32,7 @@ export class AppLightbox extends Component {
         overlay.className = "lightbox-overlay";
         overlay.setAttribute("role", "dialog");
         overlay.setAttribute("aria-modal", "true");
+        overlay.setAttribute("aria-label", "Image viewer");
         overlay.innerHTML =
             '<button type="button" class="lightbox-close" aria-label="Close">&times;</button>' +
             '<img class="lightbox-image" src="" alt="">';
@@ -53,6 +54,12 @@ export class AppLightbox extends Component {
                 this.close();
             }
         });
+        this.overlay.addEventListener("keydown", (e) => {
+            if (e.key === "Tab" && this.overlay.classList.contains("visible")) {
+                e.preventDefault();
+                this.closeBtn.focus();
+            }
+        });
         document.addEventListener("click", (e) => {
             const thumb = e.target.closest("img[data-lightbox]");
             if (!thumb || thumb.closest("a")) return;