chore: remove stray vault files from Plan 1B + add plan doc

A Task 6 implementer subagent ran `relicario init` inside the worktree
root during manual testing and committed the resulting vault skeleton
(.relicario/, manifest.enc, settings.enc) plus overwrote .gitignore.
None of these should be in the source repo.

Restores the original .gitignore (adds reference.jpg and ref.jpg to it)
and checks in the Plan 1B design doc that describes the work just merged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -1 +1,9 @@
+target/
+.superpowers/
+.worktrees/
+extension/node_modules/
+extension/dist/
+extension/dist-firefox/
+extension/wasm/
+reference.jpg
 ref.jpg

.relicario/devices.json

@@ -1 +0,0 @@
-[]

.relicario/params.json

@@ -1,11 +0,0 @@
-{
-  "format_version": 2,
-  "kdf": {
-    "algorithm": "argon2id-v0x13",
-    "argon2_m": 65536,
-    "argon2_t": 3,
-    "argon2_p": 4
-  },
-  "aead": "xchacha20poly1305",
-  "salt_path": ".relicario/salt"
-}

.relicario/salt

@@ -1 +0,0 @@
-
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