feat: native matrix URI pills for {user}/{room} + major rendering & codebase refactor

This change introduces native `matrix:` URI-based rendering for `{user}` and `{room}` placeholders,
replacing previous plaintext and matrix.to-based links. Users and rooms are now rendered as clickable
pills in supporting clients, with a clean display using display names and room names (no @/# prefixes).

Reporting, moderation, and auto-redaction messages have been updated to use the same rendering logic.
Inspect and event links now also use native `matrix:` URIs for direct in-client navigation.

Internally, URI generation and rendering logic have been unified via central helper functions,
ensuring consistent handling of user IDs, room IDs, aliases, and event IDs.

This commit also includes a broader refactor of the codebase:
- decomposed complex flows (e.g. join handling) into smaller helpers
- moved mutable class-level state to instance-level
- reduced duplicate API calls and redundant logic
- improved overall structure and maintainability

Test coverage has been extended for URI helpers and rendering logic to prevent regressions.

No breaking changes to existing template parameters like `{user_link}` or `{room_link}`.

tests/test_template_rendering.py

@@ -12,7 +12,11 @@ from community.bot import CommunityBot
 def bot():
     bot = CommunityBot.__new__(CommunityBot)
     bot.client = Mock()
-    bot.config = {"matrix_to_base_url": "https://matrix.to"}
+    bot.config = {
+        "matrix_to_base_url": "https://matrix.to",
+        "user_pill_prefix": "@",
+        "room_pill_prefix": "#",
+    }
     return bot
 
 
@@ -51,7 +55,50 @@ def test_render_message_template_supports_user_id_and_user_link(bot):
         "General",
     )
 
-    assert plain == "Alice / @alice:example.org / https://matrix.to/#/@alice:example.org"
-    assert "Alice / @alice:example.org / " in html
+    assert plain == "@Alice / @alice:example.org / https://matrix.to/#/@alice:example.org"
+    assert "@Alice / @alice:example.org / " in html
     assert '<a href=' in html
     assert '>Alice</a>' in html
+
+
+def test_render_message_template_uses_configurable_user_and_room_pill_prefixes(bot):
+    bot.config["user_pill_prefix"] = ""
+    bot.config["room_pill_prefix"] = ""
+
+    plain, html = bot._render_message_template(
+        "{user} has joined {room}.",
+        "@alice:example.org",
+        "Alice",
+        "!room:example.org",
+        "General",
+    )
+
+    assert plain == "Alice has joined General."
+    assert "<a href='matrix:u/alice:example.org?action=chat'>Alice</a>" in html
+    assert "<a href='matrix:roomid/room:example.org'>General</a>" in html
+
+
+def test_render_message_template_defaults_to_prefixed_user_and_room_pills(bot):
+    plain, html = bot._render_message_template(
+        "{user} has joined {room}.",
+        "@alice:example.org",
+        "Alice",
+        "!room:example.org",
+        "General",
+    )
+
+    assert plain == "@Alice has joined #General."
+    assert "<a href='matrix:u/alice:example.org?action=chat'>@Alice</a>" in html
+    assert "<a href='matrix:roomid/room:example.org'>#General</a>" in html
+
+
+def test_matrix_uri_helpers_are_consistent():
+    from community.bot import CommunityBot
+
+    bot = CommunityBot.__new__(CommunityBot)
+    bot.config = {}
+
+    assert bot._matrix_user_uri("@alice:example.org") == "matrix:u/alice:example.org?action=chat"
+    assert bot._matrix_room_uri("!roomid:example.org", "#general:example.org") == "matrix:r/general:example.org"
+    assert bot._matrix_room_uri("!roomid:example.org", None) == "matrix:roomid/roomid:example.org"
+    assert bot._matrix_event_uri("!roomid:example.org", "$eventid") == "matrix:roomid/roomid:example.org/e/eventid"