phase 1: stop the bleeding — untrack 91 files, add verifier, harden CI

- Remove 91 tracked-but-gitignored files from index (sessions, plugin
  data/manifests, pycache, memory-changes, obsidian state, credential
  notes). Disk files preserved via --cached.
- Add .gitignore rules: .qmd/, .memory-index.lock, *.sqlite-wal/shm,
  13 credential note paths.
- Remove filename-blacklist ignore patterns (**/*password*.md etc.)
  that caught nothing and misfired on normal notes.
- Add .scripts/verify-vault.mjs: scans git-tracked files for key
  patterns (sk-*, AKIA*, gh[pousr]_*, glpat-*, xox*, BEGIN PRIVATE
  KEY) and 64-char hex in plugin .json files.
- Add verifier step to CI lint workflow before dependency install.

.obsidian/plugins/advanced-canvas/manifest.json

@@ -1,11 +0,0 @@
-{
-  "id": "advanced-canvas",
-  "name": "Advanced Canvas",
-  "version": "6.0.0",
-  "minAppVersion": "1.1.0",
-  "description": "Supercharge your canvas experience! Create presentations, flowcharts and more!",
-  "author": "Developer-Mike",
-  "authorUrl": "https://github.com/Developer-Mike",
-  "fundingUrl": "https://ko-fi.com/X8X27IA08",
-  "isDesktopOnly": false
-}