Add space groups, fix HLTB scraper, fix quote wall E2EE, improve tarot prompts

Space groups: automatic room grouping via membership overlap percentage.
Rooms with sufficient shared members are grouped together so leaderboards,
trivia scores, and stats aggregate across the community. Uses strict
clique-based algorithm (every room must meet threshold with every other
room in group). Configurable via SPACE_GROUP_THRESHOLD env var. Persisted
to SQLite, recomputed hourly and on startup.

HLTB scraper: rewrote for new howlongtobeat.com API (two-step token auth
via /api/finder/init + /api/finder endpoint).

Quote wall: fix E2EE decrypt flow for reply-to-save (ParseRaw before
Decrypt, skip ParseRaw after Decrypt returns pre-parsed event). Fix
subcommand matching for delete/search. Remove broken star-reaction handler
and old quote handler from user.go.

Other fixes:
- Strip Matrix reply fallback before command detection (main.go)
- Increase Ollama context window to 8192
- Improve tarot spread prompts (~4x longer, narrative arc)
- Add "cards are props" instruction to tarot LLM prompt
- Fix movies.go CommandDef name mismatch
- Add Community category to !help
- Remove daily horoscope broadcast cron
- Update README with all changes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/plugin/welcome.go

@@ -118,6 +118,7 @@ var categoryOrder = []string{
 	"LLM & Sentiment",
 	"Personal",
 	"Holidays",
+	"Community",
 	"Reactions",
 	"Info",
 }
@@ -131,6 +132,7 @@ var categoryEmojis = map[string]string{
 	"LLM & Sentiment":    "🧠",
 	"Personal":           "👤",
 	"Holidays":           "🎉",
+	"Community":          "💬",
 	"Reactions":          "😎",
 	"Info":               "ℹ️",
 	"Admin":              "🔧",