ai: single-switch GPT/Claude backend for the chat cog

Wire the bot's AI chat pipeline (ai_functions.handle_response) to talk to
either OpenAI or the Anthropic Messages API, chosen by one active-config
switch. Behaviour on the default "gpt" config is unchanged.

constants.py:
* guarded `import anthropic` + CLAUDECLIENT (mirrors OPENAICLIENT), netrc
  machine 'anthropic' / ANTHROPIC_API_KEY;
* CLAUDE_LATEST_MODEL / CLAUDE_CHEAP_MODEL (opus-4-8 / haiku-4-5);
* AI_CONFIGS + DEFAULT_AI_CONFIG loaded from an optional 3rd element of
  system_gpt_settings.json (backward compatible - a 2-element file falls
  back to built-in defaults, active "gpt"). Single switch: CONJURER_AI_CONFIG
  env > settings "active" > "gpt".

ai_functions.py:
* provider_generate() dispatches to OpenAI (unchanged openai_call) or the new
  _anthropic_call() (splits system out, alternating messages, max_tokens,
  temperature omitted - Opus 4.8 rejects sampling params);
* AIError normalises both SDKs' exceptions into one category set so
  handle_response keeps its single set of in-character error replies;
* select_model() reads the active config; legacy "gpt-4o" default auto-maps
  to the active provider's model so the switch actually changes the backend;
* set_active_ai_config()/list_ai_configs() with best-effort persistence back
  into system_gpt_settings.json index 2.

ai_commands.py:
* $gadaj_teraz <config> hybrid command (Vykidailo-gated) switches backend at
  runtime;
* graceful guards when OPENAICLIENT is None: personal assistants (OpenAI
  Assistants API) and DALL-E image gen degrade instead of crashing, so a
  Claude-only deployment boots.

system_gpt_settings.json: add the configs block (gpt/claude/_template) as the
collection point for future backends. requirements_bot.txt: add anthropic.
bot.env.example: ANTHROPIC_API_KEY + CONJURER_AI_CONFIG. Unit tests cover the
message splitter, model selection, config listing, and error mapping.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

constants.py

@@ -38,6 +38,11 @@ try:
 except ImportError:  # pragma: no cover - optional at runtime
     openai = None
 
+try:
+    import anthropic
+except ImportError:  # pragma: no cover - optional at runtime
+    anthropic = None
+
 try:
     import spotipy
     from spotipy.oauth2 import SpotifyClientCredentials
@@ -336,6 +341,15 @@ if openai and OPENAI_API_KEY:
 else:
     OPENAICLIENT = None
 
+# Claude / Anthropic client, wired analogously to OpenAI above so the AI cog can
+# be pointed at either backend with a single config switch (see AI_CONFIGS and
+# ai_functions.set_active_ai_config). netrc machine name 'anthropic' works too.
+ANTHROPIC_API_KEY = _resolve_token("anthropic", "ANTHROPIC_API_KEY")
+if anthropic and ANTHROPIC_API_KEY:
+    CLAUDECLIENT = anthropic.AsyncAnthropic(api_key=ANTHROPIC_API_KEY)
+else:
+    CLAUDECLIENT = None
+
 TOKEN = _resolve_token("discord", "DISCORD_TOKEN")
 
 # Voice recognition (AssemblyAI). None = the voice cog reports and disables.
@@ -388,6 +402,75 @@ GUILD_ID = 664789470779932693
 LATEST_MODEL = "gpt-4o"          # najnowszy/do rozmów (możesz zmienić w jednym miejscu)
 CHEAP_MODEL  = "gpt-4o-mini"     # najtańszy (fallback do 3.5 niżej)
 
+# Claude counterparts of LATEST_MODEL / CHEAP_MODEL. Opus 4.8 is the strongest
+# widely available model; Haiku 4.5 is the fast/cheap tier used for MUSIC.
+CLAUDE_LATEST_MODEL = "claude-opus-4-8"
+CLAUDE_CHEAP_MODEL  = "claude-haiku-4-5"
+
+
+# *=========================================== AI provider configs
+# The bot's AI functionality (ai_functions.handle_response) can be pointed at a
+# different backend by flipping a single "active" switch. Each named config
+# collects the *differences* between providers (which backend, which models,
+# generation params). These live in system_gpt_settings.json under an optional
+# third list element (index 2) so future configs are simply added there:
+#
+#   [ <system message>, <personal assistants>, { "active": "gpt",
+#                                                 "configs": { ... } } ]
+#
+# The block is optional and backward compatible: a settings file with only the
+# original two elements falls back to the built-in defaults below (active
+# "gpt"), so existing deployments behave exactly as before. The active config
+# can be overridden at import time with CONJURER_AI_CONFIG and at runtime with
+# the $gadaj_teraz command (which persists the choice back into index 2).
+def _default_ai_configs():
+    return {
+        "gpt": {
+            "provider": "openai",
+            "latest_model": LATEST_MODEL,
+            "cheap_model": CHEAP_MODEL,
+            "temperature": 0.2,
+        },
+        "claude": {
+            "provider": "anthropic",
+            "latest_model": CLAUDE_LATEST_MODEL,
+            "cheap_model": CLAUDE_CHEAP_MODEL,
+            # Anthropic requires max_tokens; temperature is intentionally not
+            # sent for Claude (Opus 4.8 / Sonnet 5 reject sampling params).
+            "max_tokens": 2048,
+        },
+        # Template for wiring further providers. Copy it, rename the key, point
+        # "provider" at a backend ai_functions.provider_generate implements, and
+        # fill in the model ids. Keys starting with "_" are treated as inert
+        # templates and are hidden from the $gadaj_teraz picker.
+        "_template": {
+            "provider": "openai",
+            "latest_model": "model-id-here",
+            "cheap_model": "cheaper-model-id-here",
+            "temperature": 0.2,
+            "max_tokens": 2048,
+        },
+    }
+
+
+_ai_block = (
+    GPT_SETTINGS[2]
+    if isinstance(GPT_SETTINGS, list) and len(GPT_SETTINGS) > 2 and isinstance(GPT_SETTINGS[2], dict)
+    else {}
+)
+AI_CONFIGS = _ai_block.get("configs") or _default_ai_configs()
+# Single switch: env var wins, then the settings-file "active" key, then "gpt".
+DEFAULT_AI_CONFIG = (
+    os.getenv("CONJURER_AI_CONFIG")
+    or _ai_block.get("active")
+    or "gpt"
+)
+if DEFAULT_AI_CONFIG not in AI_CONFIGS:
+    logger.warning(
+        "AI config '%s' not found - falling back to 'gpt'", DEFAULT_AI_CONFIG
+    )
+    DEFAULT_AI_CONFIG = "gpt" if "gpt" in AI_CONFIGS else next(iter(AI_CONFIGS))
+
 
 # *=========================================== Conan Exiles bridge
 # Every value is optional; the conanjurer cog stays dormant unless configured.