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/utils.ts

@@ -41,9 +41,7 @@ export function debounce<T extends (...args: never[]) => void>(fn: T, wait = 300
 	}) as T;
 }
 
-// eslint-disable-next-line @typescript-eslint/no-explicit-any
-export type WithoutChild<T> = T extends { child?: any } ? Omit<T, "child"> : T;
-// eslint-disable-next-line @typescript-eslint/no-explicit-any
-export type WithoutChildren<T> = T extends { children?: any } ? Omit<T, "children"> : T;
+export type WithoutChild<T> = T extends { child?: unknown } ? Omit<T, "child"> : T;
+export type WithoutChildren<T> = T extends { children?: unknown } ? Omit<T, "children"> : T;
 export type WithoutChildrenOrChild<T> = WithoutChildren<WithoutChild<T>>;
 export type WithElementRef<T, U extends HTMLElement = HTMLElement> = T & { ref?: U | null };