wave 2 (platform stream): settings storage & plumbing foundation (P2)

- src/core/settings.ts: versioned DELTA record schema + sanitizer (unknown keys preserved)
  — general/chat/agent{models,tools,prompts}/appearance/graph sections
- src/core/settings-resolution.ts: pure resolveSettings (factory defaults → user delta),
  extraction/graph-context channel predicates
- src/store/settings.ts + prompt-overrides.ts: SettingsStore/PromptOverrideStore adapters
  wired through stores.ts (effectiveSettings() fresh per call); lazy migration of
  default-settings.json into record.chat
- app/api/settings/** routes (record, section bodies, prompt overrides per segment)
- chat-handler: graph gates at trigger call-sites + toolToggles injection seam
- config.ts: SETTINGS_FILE + PROMPTS_OVERRIDE_DIR paths

587/587 tests; typecheck/lint/build clean

src/core/index.ts

@@ -34,6 +34,11 @@ export * from "./ui-message.ts";
 export * from "./tool-parts.ts";
 export * from "./prices.ts";
 export * from "./fuzzy.ts";
+// settings.ts + settings-resolution.ts (settings-storage wave, 2026-09-19):
+// the user-settings record's shape/sanitizer (pure) and its fully-resolved
+// view. Browser-safe — the Wave-4 panel imports these directly.
+export * from "./settings.ts";
+export * from "./settings-resolution.ts";
 // keyboard.ts: the shortcut registry + binding normalization (pure, browser-safe).
 export * from "./keyboard.ts";
 export * from "./coverage.ts";