feat(web): define ChatEvent discriminated union, eliminate all any sites (R9)

Created web/src/lib/types.ts with discriminated unions for SSE event
payloads: ChatEvent (7 variants: session, tool_use, tool_result,
text_delta, text, done, error), ToolCallResult, MessageContent, and
typed data shapes for live events (PlanProposedData, PlanStepEventData,
QuestionRaisedData, QuestionAnsweredData, EntityTouchedData,
HealthChangedData) plus WailsGlobal for the desktop bridge.

Replaced all ~15 `any` sites across 7 files:
- api.ts: Message.content any -> MessageContent | string; removed local
  ChatEvent interface (now imported from types.ts as a discriminated
  union); JSON.parse cast to ChatEvent.
- stores/chat.ts: removed local ToolCallResult interface (imported from
  types.ts, re-exported for backward compat); extractApprovals accesses
  args with typeof guards instead of implicit any access; toChatMessages
  handles string|object Message.content cleanly.
- stores/activity.ts: update_plan_step seq/status extracted via typeof
  guards instead of `as any` casts; toolActivityLabel uses a str() helper
  for safe string extraction from unknown args.
- stores/workspace.ts: applyPlanStepEvent takes PlanStepEventData;
  applyEvent casts data to Record<string, unknown>; switch cases cast to
  typed interfaces (PlanProposedData, QuestionRaisedData, etc.) instead
  of `as any`; applyHealthChanged uses HealthChangedData.
- Config.svelte: (window as any).wails -> typed WailsGlobal cast;
  catch (e: any) -> catch (e: unknown) with instanceof Error check.
- utils.ts: WithoutChild/WithoutChildren `any` -> `unknown`.
- vite.config.ts: authProxy proxy/proxyReq `any` -> ProxyOptions type.

Result: eslint no-explicit-any warnings dropped 12 -> 0. Tests (6/6) and
build pass. VERSION 0.7.10 -> 0.7.11. Plan R9 marked done.

web/src/lib/stores/chat.ts

@@ -1,6 +1,9 @@
 import { writable, get } from 'svelte/store'
 import { streamChat, fetchSessions, fetchMessages, deleteSession as apiDeleteSession } from '$lib/api'
 import type { ChatEvent, Session, Message } from '$lib/api'
+import type { ToolCallResult } from '$lib/types'
+
+export type { ToolCallResult }
 
 export interface PendingApproval {
   executionId: string
@@ -38,28 +41,21 @@ function extractApprovals(tools: ToolCallResult[]): PendingApproval[] {
     if (!text.includes('requires approval')) continue
     const m = text.match(APPROVAL_RE)
     if (m) {
+      const args = t.args ?? {}
+      const purpose = typeof args.purpose === 'string' ? args.purpose : undefined
       out.push({
         executionId: m[1],
-        action: t.args?.purpose?.slice(0, 60) ?? t.args?.action ?? t.name ?? 'unknown',
-        target: t.args?.target ?? 'unknown',
+        action: purpose ? purpose.slice(0, 60) : typeof args.action === 'string' ? args.action : t.name,
+        target: typeof args.target === 'string' ? args.target : 'unknown',
         destructive: /\bDESTRUCTIVE\b/.test(text),
-        command: t.args?.command,
-        purpose: t.args?.purpose
+        command: typeof args.command === 'string' ? args.command : undefined,
+        purpose
       })
     }
   }
   return out
 }
 
-export interface ToolCallResult {
-  type: 'tool_use' | 'tool_result'
-  name: string
-  id?: string
-  args?: any
-  result?: any
-  error?: string
-}
-
 function mid(): string {
   return crypto.randomUUID()
 }
@@ -119,11 +115,12 @@ function mergeToolCalls(raw: ToolCallResult[] | undefined): ToolCallResult[] {
 
 function toChatMessages(msgs: Message[]): ChatMessage[] {
   return msgs.map((m) => {
-    const tools = mergeToolCalls(m.content?.tool_calls)
+    const content = typeof m.content === 'string' ? { text: m.content } : m.content
+    const tools = mergeToolCalls(content?.tool_calls)
     return {
       id: m.id,
       role: m.role as 'user' | 'assistant',
-      text: m.content?.text ?? (typeof m.content === 'string' ? m.content : ''),
+      text: content?.text ?? '',
       tools,
       pendingApprovals: extractApprovals(tools)
     }