feat(compression): add settings API route for compression configuration

Add GET/PUT /api/settings/compression with authentication, Zod body validation (enabled, defaultMode, autoTriggerTokens, cacheMinutes, preserveSystemPrompt, comboOverrides). Follows existing settings route pattern.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/app/api/settings/compression/route.ts

@@ -0,0 +1,58 @@
+import { NextRequest, NextResponse } from "next/server";
+import { z } from "zod";
+import { isAuthenticated } from "@/shared/utils/apiAuth";
+import { isValidationFailure, validateBody } from "@/shared/validation/helpers";
+import { getCompressionSettings, updateCompressionSettings } from "@/lib/db/compression";
+
+const compressionModeSchema = z.enum(["off", "lite", "standard", "aggressive", "ultra"]);
+
+const compressionSettingsUpdateSchema = z
+  .object({
+    enabled: z.boolean().optional(),
+    defaultMode: compressionModeSchema.optional(),
+    autoTriggerTokens: z.number().int().min(0).optional(),
+    cacheMinutes: z.number().int().min(1).max(60).optional(),
+    preserveSystemPrompt: z.boolean().optional(),
+    comboOverrides: z.record(z.string(), compressionModeSchema).optional(),
+  })
+  .strict();
+
+export async function GET(request: NextRequest) {
+  if (!(await isAuthenticated(request))) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  try {
+    const settings = await getCompressionSettings();
+    return NextResponse.json(settings);
+  } catch (error) {
+    return NextResponse.json({ error: String(error) }, { status: 500 });
+  }
+}
+
+export async function PUT(request: NextRequest) {
+  if (!(await isAuthenticated(request))) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  try {
+    let rawBody: unknown;
+    try {
+      rawBody = await request.json();
+    } catch {
+      return NextResponse.json({ error: "Invalid JSON body" }, { status: 400 });
+    }
+
+    const validation = validateBody(compressionSettingsUpdateSchema, rawBody);
+    if (isValidationFailure(validation)) {
+      return NextResponse.json({ error: validation.error }, { status: 400 });
+    }
+
+    const settings = await updateCompressionSettings(
+      validation.data as Parameters<typeof updateCompressionSettings>[0]
+    );
+    return NextResponse.json(settings);
+  } catch (error) {
+    return NextResponse.json({ error: String(error) }, { status: 500 });
+  }
+}