feat(ai-chat): header badge shows current/max context, max from AI settings (#189)

The floating chat window's header badge flipped meaning — a live per-turn token
counter while streaming, the persisted context size at rest — so it "reset to 1"
on each prompt and conflated two different numbers. Replace it with a stable
"current / max" context badge (e.g. `572 / 200k`). The live "Thinking · N tokens"
inside the chat body stays; only the duplicate live counter is removed from the
header.

Max comes from a new admin setting "Context window (tokens)". The server resolves
it and attaches `maxContextTokens` to the completed assistant turn's metadata
(next to contextTokens), so the badge needs no client-side model resolution and
this survives public shares / per-role models.

Server:
- ai.types: chatContextWindow on AiProviderSettings + PROVIDER_SETTINGS_KEYS +
  ResolvedAiConfig + MaskedAiSettings.
- workspace.repo: chatContextWindow in AI_PROVIDER_SETTINGS_ALLOWED (parity).
- update-ai-settings.dto: @IsInt @Min(0) chatContextWindow.
- ai-settings.service: coerce the ::text-stored value to a positive int in
  resolve()/getMasked().
- ai-chat.service: flushAssistant writes metadata.maxContextTokens (>0); the
  completed turn passes resolved.chatContextWindow.

Client:
- ai-chat.types: maxContextTokens on the message-row metadata.
- ai-chat-window: read maxContextTokens; render "current [/ max]"; drop the
  liveTurnTokens state/branch and the onLiveTurnTokens prop; new tooltip.
- chat-thread: remove the live-turn-token throttle effect and plumbing.
- count-stream-tokens: drop the now-dead liveTurnTokens()/types; keep
  estimateTokens.
- settings: chatContextWindow on IAiSettings(+Update) + a NumberInput in the AI
  provider settings form.

i18n: add the badge/settings keys (en, ru); remove the two now-unused keys.
Tests: flushAssistant maxContextTokens, DTO validation, trim token tests.

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

apps/client/src/features/workspace/components/settings/components/ai-provider-settings.tsx

@@ -7,6 +7,7 @@ import {
   Button,
   Group,
   Modal,
+  NumberInput,
   Paper,
   PasswordInput,
   Select,
@@ -83,6 +84,9 @@ const STT_LANGUAGE_OPTIONS: { value: string; label: string }[] = [
 // (empty means "leave unchanged" unless explicitly cleared).
 const formSchema = z.object({
   chatModel: z.string(),
+  // Max context window in tokens shown in the chat header badge. A number, or ""
+  // when the NumberInput is empty (no limit).
+  chatContextWindow: z.union([z.number(), z.literal("")]),
   // Chat provider implementation (reasoning surfacing). Default openai-compatible.
   chatApiStyle: z.enum(["openai-compatible", "openai"]),
   // Cheap model id for the anonymous public-share assistant; empty = use chatModel.
@@ -311,6 +315,7 @@ export default function AiProviderSettings() {
     validate: zod4Resolver(formSchema),
     initialValues: {
       chatModel: "",
+      chatContextWindow: "",
       chatApiStyle: "openai-compatible" as ChatApiStyle,
       publicShareChatModel: "",
       publicShareAssistantRoleId: "",
@@ -334,6 +339,7 @@ export default function AiProviderSettings() {
     if (!settings) return;
     form.setValues({
       chatModel: settings.chatModel ?? "",
+      chatContextWindow: settings.chatContextWindow ?? "",
       chatApiStyle: settings.chatApiStyle ?? "openai-compatible",
       publicShareChatModel: settings.publicShareChatModel ?? "",
       publicShareAssistantRoleId: settings.publicShareAssistantRoleId ?? "",
@@ -364,6 +370,12 @@ export default function AiProviderSettings() {
       // Everything is OpenAI-compatible.
       driver: "openai",
       chatModel: values.chatModel,
+      // Max context window for the chat header badge; empty NumberInput ("") →
+      // 0, which clears the limit server-side (no denominator shown).
+      chatContextWindow:
+        typeof values.chatContextWindow === "number"
+          ? values.chatContextWindow
+          : 0,
       chatApiStyle: values.chatApiStyle,
       // Cheap model id for the anonymous public-share assistant; empty falls
       // back to chatModel server-side.
@@ -767,6 +779,18 @@ export default function AiProviderSettings() {
           {t("Resolves to {{url}}", { url: chatResolved })}
         </Text>
 
+        <NumberInput
+          mt="sm"
+          label={t("Context window (tokens)")}
+          description={t(
+            "Shown as used / total in the chat header. Leave empty to hide the limit.",
+          )}
+          min={0}
+          allowDecimal={false}
+          disabled={isLoading}
+          {...form.getInputProps("chatContextWindow")}
+        />
+
         <Select
           mt="sm"
           label={t("Protocol")}