feat(companion): Dross persona (Cradle) + migration 008 rename; remove dead API-key path

- system prompt = Dross (Ozriel's construct fragment, per Void 1.0), with tool guidance
- migration 008 renames the seeded agent 'companion' → display name 'Dross'
- removed lib/ai/anthropic.js + lib/ai/agent/runtime.js + tests + @anthropic-ai/sdk dep (companion now runs via the claude CLI; kept lib/ai/secret.js for the Vaultwarden roadmap)

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

lib/ai/agent/runtime.js

@@ -1,58 +0,0 @@
-// Tool-use loop. callModel + registry injected (no network here).
-// Emits: { type:'tool', tool, args, status } | { type:'delta', text }
-//        | { type:'draft', pending_change_id, summary }
-// Returns: { text, toolTrace, draftIds, usage, stoppedOnGuard }
-export async function runTurn({ callModel, registry, system, messages, ctx, onEvent, maxIterations = 6 }) {
-  const convo = [...messages];
-  const toolTrace = [];
-  const draftIds = [];
-  let usage = {};
-  let stoppedOnGuard = false;
-
-  for (let i = 0; i < maxIterations; i++) {
-    const res = await callModel({
-      system,
-      messages: convo,
-      tools: registry.toAnthropicTools(),
-      onTextDelta: (t) => onEvent?.({ type: 'delta', text: t })
-    });
-    usage = res.usage || usage;
-
-    if (!res.toolUses?.length) {
-      return { text: res.text, toolTrace, draftIds, usage, stoppedOnGuard };
-    }
-
-    // Record the assistant turn (text + tool_use blocks) for the next round.
-    convo.push({
-      role: 'assistant',
-      content: [
-        ...(res.text ? [{ type: 'text', text: res.text }] : []),
-        ...res.toolUses.map(t => ({ type: 'tool_use', id: t.id, name: t.name, input: t.input }))
-      ]
-    });
-
-    const toolResults = [];
-    for (const call of res.toolUses) {
-      const tool = registry.getTool(call.name);
-      let result;
-      try {
-        result = tool ? await tool.handler(call.input, ctx) : { error: `unknown tool ${call.name}` };
-      } catch (e) {
-        result = { error: String(e?.message || e) };
-      }
-      const status = result?.error ? 'error' : 'done';
-      toolTrace.push({ tool: call.name, args: call.input, ok: !result?.error });
-      onEvent?.({ type: 'tool', tool: call.name, args: call.input, status });
-      if (result?.pending_change_id) {
-        draftIds.push(result.pending_change_id);
-        onEvent?.({ type: 'draft', pending_change_id: result.pending_change_id, summary: result.summary });
-      }
-      toolResults.push({ type: 'tool_result', tool_use_id: call.id, content: JSON.stringify(result) });
-    }
-    convo.push({ role: 'user', content: toolResults });
-
-    if (i === maxIterations - 1) stoppedOnGuard = true;
-  }
-
-  return { text: '', toolTrace, draftIds, usage, stoppedOnGuard };
-}