feat: smart video size warnings + Jinja2 template autocomplete

Video size warnings:
- Add file_size field to ImmichAssetInfo from exifInfo.fileSizeInByte
- Expose per-target max_video_size (50 MB for Telegram, none for others)
- Compute has_oversized_videos and per-asset oversized flag in template context
- Default templates show warning only when videos actually exceed the limit
- Templates no longer hardcode Telegram-specific logic

Template autocomplete:
- New jinja-autocomplete.ts engine with contextual completions
- Top-level variables ({{ }}), asset/album fields (dot access in loops),
  Jinja2 filters (|), block tags ({% %}), and loop.* special vars
- JinjaEditor accepts optional variables prop via CodeMirror Compartment
- Wired into template-configs and command-template-configs pages

Also: fix template emoji (📷 → 📎) and sync sample_context with new vars.

frontend/src/routes/command-template-configs/+page.svelte

@@ -305,6 +305,7 @@
 							onchange={(v: string) => { setSlotValue(slot.name, v); validateSlot(slot.name, v); }}
 							rows={3}
 							errorLine={slotErrorLines[slot.name] || null}
+							variables={varsRef[slot.name] || undefined}
 						/>
 						{#if slotErrors[slot.name]}
 							{#if slotErrorTypes[slot.name] === 'undefined'}