feat(markdown): render TikZ fenced blocks to SVG

Adds a markdown-it extractor for ```tikz blocks that emits a sanitized
placeholder, plus a runTikz() that lazy-loads the obsidian-tikzjax 0.5.2
bundle from jsdelivr on first encounter, sanitizes the produced SVG with
DOMPurify, and caches it in PouchDB keyed by sha256(source) so repeat
views are instant and offline-capable.

src/data/DataType.enum.ts

@@ -7,5 +7,6 @@ export enum DataType {
   RepetitionCard = "RepetitionCard",
   History = "History",
   UserSettings = "UserSettings",
-  AtprotoSession = "AtprotoSession"
+  AtprotoSession = "AtprotoSession",
+  TikzCache = "TikzCache"
 }