docs: update architecture notes and TODO with Svelte 5 store migration plan

- AE__Architecture.md: minor wording fix
- TODO__Agents.md: add Svelte 4→5 store migration task (root cause of IDAA
  Novi re-auth bug; prerequisite for Phase 2c store refactor)
- PROJECT__Stores_Svelte5_Migration.md: new migration planning doc

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

documentation/PROJECT__Stores_Svelte5_Migration.md

@@ -0,0 +1,97 @@
+# Project: Svelte 4 Store → Svelte 5 State Migration
+
+**Status:** Execution / Phase B (In Progress)
+**Priority:** High (post-April 2026 conference)
+**Created:** 2026-03-30
+**Related:** `TODO__Agents.md` — [Stores] Svelte 5 State Migration entry
+
+---
+
+## Background
+
+All core Aether stores (`ae_loc`, `idaa_loc`, `ae_events_loc`, etc.) are being migrated from 
+Svelte 4 stores to Svelte 5 `$state` using the `runed` library's `PersistedState`. This provides 
+fine-grained reactivity, ensuring that effects only re-run when specific fields they access are 
+updated, rather than on every write to the store object.
+
+### Phase B Progress & Learnings (Updated 2026-03-30)
+
+1. **Dependency Installed**: `runed` is now a project dependency.
+2. **Module Resolution Strategy**: 
+   - Core store files renamed: `ae_stores.ts` → `ae_stores.svelte.ts`, etc.
+   - **Critical Discovery**: SvelteKit and CLI tools (`svelte-check`) struggled to resolve 
+     extension-less imports (like `$lib/stores/ae_stores`) when only `.svelte.ts` existed.
+   - **Solution**: Created `.ts` wrapper files (e.g., `src/lib/stores/ae_stores.ts`) that 
+     simply re-export everything via `export * from './ae_stores.svelte'`. This maintains 
+     backward compatibility for all existing import paths without manual updates.
+3. **API Confirmation**: Confirmed that `runed`'s `PersistedState` uses `.current` to access 
+   the state object, matching the intended migration syntax.
+4. **Mass Replacement**: 
+   - `$ae_loc` → `ae_loc_v5.current`
+   - `$idaa_loc` → `idaa_loc_v5.current`
+   - `$events_loc` → `events_loc_v5.current`
+   - These replacements have been applied across the entire `src/` directory (~2000+ sites).
+5. **Import Updates**: A robust Python script was used to surgically add `ae_loc_v5`, 
+   `idaa_loc_v5`, and `events_loc_v5` to existing import blocks, avoiding `import type` 
+   lines and duplicates.
+
+---
+
+## Syntax Changes: Before / After
+
+### Store declaration
+
+```typescript
+// BEFORE (ae_stores.svelte.ts)
+export const ae_loc: Writable<key_val> = persisted('ae_loc', defaults);
+
+// AFTER (ae_stores.svelte.ts)
+export const ae_loc_v5 = new PersistedState('ae_loc', defaults);
+```
+
+### Reading/Writing (Consumers)
+
+```svelte
+<!-- BEFORE -->
+{$ae_loc.theme_mode}
+{#if $ae_loc.trusted_access}
+
+<!-- AFTER -->
+{ae_loc_v5.current.theme_mode}
+{#if ae_loc_v5.current.trusted_access}
+```
+
+### Batch Update Pattern
+
+```typescript
+// Use Object.assign for multi-field updates to maintain fine-grained reactivity
+Object.assign(ae_loc_v5.current, { theme_mode: 'dark', edit_mode: true });
+```
+
+---
+
+## Implementation Notes
+
+### Prettier & Formatting
+Because the mass migration touches ~250 files, formatting may be inconsistent (especially in 
+import blocks). It is recommended to run `npm run format` (if available) or rely on standard 
+linting after the imports are stabilized.
+
+### Batching vs. "Big Sweep"
+While the original plan suggested smaller batches, the global nature of `ae_loc` and the 
+hundreds of interdependent files made a "Big Sweep" more efficient to ensure the app remains 
+in a consistent state. However, verification should still be done module-by-module.
+
+---
+
+## Current Status (Pause Point)
+
+- [x] Phase A: Plan written.
+- [x] Phase B: Core infrastructure setup (runed, renames, wrappers).
+- [x] Phase B: Mass variable replacement ($ae_loc -> ae_loc_v5.current).
+- [/] Phase B: Mass import update (In Progress/Verifying).
+- [ ] Phase B: Final validation (`svelte-check` clean).
+
+**Do NOT stage or commit until `npx svelte-check` is fully verified.**
+The app currently has a high error count due to the transition period where imports are being 
+re-aligned. Final verification is the next step after the pause.