Fix template variable docs to match actual notifier output

Audit and fix all template variable references:
- template_vars.py: Add missing fields (album_id, old_shared,
  new_shared, latitude, longitude, owner_id, people per asset)
- _SAMPLE_CONTEXT: Use proper structured data matching
  build_asset_detail() output (id, owner_id, latitude, longitude,
  people per asset, playback_url for videos)
- i18n: Fix all variable descriptions for accuracy, add missing
  fields, mark scheduler-dependent slots as "not yet implemented"
- Variables modal: Add album_fields section for periodic_summary
- Shared _ASSET_FIELDS and _ALBUM_FIELDS dicts in template_vars.py
  to keep scheduled/memory slots DRY

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

plans/phase-11-snackbar-notifications.md

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+# Phase 11: Snackbar Notifications
+
+**Status**: Pending
+**Parent**: [primary-plan.md](primary-plan.md)
+
+---
+
+## Goal
+
+Replace browser `alert()` calls, silent failures, and inconsistent error handling with a unified snackbar/toast notification system. Every user-triggered action (save, delete, test, etc.) should provide clear visual feedback via a dismissable snackbar that appears at the bottom of the screen.
+
+---
+
+## Design
+
+### Snackbar Types
+
+| Type | Color | Icon | Auto-dismiss | Use Case |
+|---|---|---|---|---|
+| `success` | Green | `mdiCheckCircle` | 3s | Save, delete, test passed |
+| `error` | Red | `mdiAlertCircle` | 5s (or manual) | API errors, validation failures |
+| `info` | Blue | `mdiInformation` | 3s | Status updates, copy-to-clipboard |
+| `warning` | Amber | `mdiAlert` | 4s | Non-critical issues, deprecation notices |
+
+### Behavior
+
+- Appears at bottom-center of viewport, above the mobile nav bar
+- Stacks vertically (newest on top, max 3 visible)
+- Slide-up entrance, fade-out exit animation
+- Manual dismiss via X button on all types
+- Errors with detail: expandable to show full error message
+- `position: fixed` with inline styles (per project convention)
+
+---
+
+## Implementation Plan
+
+### Task 1: Create Snackbar Store + Component
+
+**Files to create:**
+- `frontend/src/lib/stores/snackbar.svelte.ts` — reactive store using `$state`
+  - `addSnack(type, message, options?)` — push notification
+  - `removeSnack(id)` — dismiss
+  - `snacks` — reactive array of active notifications
+  - Auto-dismiss timer per snack
+
+- `frontend/src/lib/components/Snackbar.svelte` — renders snack stack
+  - Fixed position at bottom-center
+  - Svelte transitions (fly + fade)
+  - Icon per type, dismiss button, optional detail expand
+  - Responsive: full-width on mobile, max-width on desktop
+
+### Task 2: Mount Snackbar in Layout
+
+**Files to modify:**
+- `frontend/src/routes/+layout.svelte` — add `<Snackbar />` component (renders globally)
+
+### Task 3: Replace All Alert/Silent Patterns
+
+**Files to modify (each page):**
+
+| Page | Current Pattern | Replace With |
+|---|---|---|
+| `servers/+page.svelte` | `alert()` on error, silent success | `snack.success('Server saved')`, `snack.error(err.message)` |
+| `trackers/+page.svelte` | `alert()` on error, silent success | `snack.success('Tracker created')`, etc. |
+| `targets/+page.svelte` | `alert()` on error, silent success | `snack.success('Target saved')`, `snack.error(...)` |
+| `template-configs/+page.svelte` | `alert()` on error, silent success | `snack.success('Template saved')`, etc. |
+| `tracking-configs/+page.svelte` | `alert()` on error, silent success | `snack.success('Config saved')`, etc. |
+| `telegram-bots/+page.svelte` | `alert()` on error, silent success | `snack.success('Bot registered')`, etc. |
+| `users/+page.svelte` | `alert()` on error, silent success | `snack.success('User updated')`, etc. |
+| `login/+page.svelte` | `alert()` on error | `snack.error('Invalid credentials')` |
+
+### Task 4: Add i18n Keys
+
+**Files to modify:**
+- `frontend/src/lib/i18n/en.json` — add `snack.*` keys for all messages
+- `frontend/src/lib/i18n/ru.json` — Russian translations
+
+### Task 5: Add Snackbar to API Helper
+
+**Files to create/modify:**
+- Consider a shared `api.ts` helper that wraps `fetch()` and auto-shows error snackbars on non-2xx responses, reducing boilerplate in each page.
+
+---
+
+## Acceptance Criteria
+
+- [ ] Every create/update/delete action shows a success snackbar
+- [ ] Every API error shows an error snackbar with the server's message
+- [ ] No remaining `alert()` calls in the codebase
+- [ ] Snackbars auto-dismiss (success: 3s, error: 5s)
+- [ ] Snackbars are accessible (role="alert", aria-live)
+- [ ] Stacking works correctly (max 3, newest on top)
+- [ ] Animations are smooth (slide-up in, fade out)
+- [ ] Mobile: snackbar appears above bottom nav bar
+- [ ] All snackbar messages are i18n'd (EN + RU)