feat(llm): add BYOK tier + 4 provider adapters (OpenAI, Anthropic, Gemini, Mistral)

Phase 1-3 of BYOK support. Introduces a 5th LLM tier 'byok' that
routes to user-provided API keys via direct browser fetches.

shared-llm additions:
- LlmTier extended with 'byok' (rank 3, between mana-server and cloud)
- ByokBackend: LlmBackend implementation that delegates key lookup
  to an app-provided resolver callback, then dispatches to the right
  provider adapter
- 4 provider adapters:
  - OpenAI (gpt-5, gpt-4o, o1 family)
  - Anthropic (Claude Opus/Sonnet/Haiku 4.6) with CORS header
  - Gemini (2.5 Pro/Flash) — REST API with different message format
  - Mistral — OpenAI-compatible, reuses shared openai-compat adapter
- Pricing table for 20+ models with USD per 1M tokens
- estimateCost() + formatCost() helpers

Keys stay device-local (IndexedDB in next phase). Browser-direct
fetches mean keys never touch Mana's server.

Updates two existing tier maps (memoro DetailView, SourceBadge) to
include the new tier.

Planning doc at docs/architecture/BYOK_PLAN.md.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/mana/apps/web/src/lib/components/llm/SourceBadge.svelte

@@ -14,7 +14,7 @@
 	 *   <SourceBadge tier={result.source} latencyMs={result.latencyMs} />
 	 */
 	import { llmSettingsState, tierLabel, type LlmTier } from '@mana/shared-llm';
-	import { Lightning, Cpu, HardDrive, Cloud } from '@mana/shared-icons';
+	import { Lightning, Cpu, HardDrive, Cloud, Key } from '@mana/shared-icons';
 
 	interface Props {
 		tier: LlmTier;
@@ -39,6 +39,10 @@
 			color: 'border-blue-500/40 bg-blue-500/10 text-blue-600 dark:text-blue-400',
 			icon: HardDrive, // our infrastructure
 		},
+		byok: {
+			color: 'border-violet-500/40 bg-violet-500/10 text-violet-600 dark:text-violet-400',
+			icon: Key, // user-supplied key
+		},
 		cloud: {
 			color: 'border-amber-500/40 bg-amber-500/10 text-amber-600 dark:text-amber-400',
 			icon: Cloud, // remote

apps/mana/apps/web/src/lib/modules/memoro/views/DetailView.svelte

@@ -23,6 +23,7 @@
 		none: 'Lokal (regelbasiert)',
 		browser: 'Auf deinem Gerät (Gemma 4 E2B)',
 		'mana-server': 'Mana-Server (Gemma 4 E4B)',
+		byok: 'Dein API-Key',
 		cloud: 'Google Gemini',
 	};