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/docs_prose.py

@@ -2,6 +2,7 @@
 
 import html
 import re
+from functools import lru_cache
 
 import mistune
 
@@ -16,9 +17,14 @@ _RENDER_BLOCK = re.compile(
 )
 
 
+@lru_cache(maxsize=512)
+def _render_markdown(source: str) -> str:
+    return _markdown(source)
+
+
 def _convert(match: re.Match) -> str:
     source = html.unescape(match.group(1)).strip()
-    return f'<div class="docs-content">{_markdown(source)}</div>'
+    return f'<div class="docs-content">{_render_markdown(source)}</div>'
 
 
 def render_prose(slug: str, context: dict) -> str: