Rewrite as user-agnostic "quicksilver" plugin

Rename echo-memory/ECHO -> quicksilver/Quicksilver throughout and make the
plugin self-configuring per operator:

- First-run flow: prompt for endpoint FQDN, API key, and operator name/role;
  verify; persist to a local config file (~/.quicksilver/quicksilver-config.json).
- Two-layer setup detection: local config (is this install configured?) +
  in-vault marker (is the vault scaffolded?). Key never stored in the vault.
- Replace hardcoded endpoint/key in all curl examples with $BASE/$AUTH loaded
  from the config file.
- Genericize all "Jason"/"Bryan goldbrain"/MPM/wISP references to "the operator";
  keep Jason as architect credit (README + plugin.json author).
- Personalize memory to the configured operator (name/role seeded into
  operator-preferences and the vault marker).
- Add echo-vault.md -> quicksilver-vault.md rename migration.
- Rebuild packaged quicksilver.plugin; add docs/quicksilver-plan.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

quicksilver.plugin.src/.claude-plugin/plugin.json

@@ -0,0 +1,15 @@
+{
+  "name": "quicksilver",
+  "version": "0.6.0",
+  "description": "Persistent memory via a Quicksilver Obsidian vault over the Local REST API. Self-bootstrapping: the plugin carries the full vault scaffold and all control logic (no in-vault routing docs), so it stands up an empty vault and ports cleanly to any other. On first run it prompts the operator for the API endpoint, key, and identity, stores them in a local config file, and personalizes memory to that operator. Reads and writes notes across Claude/CoWork sessions using direct REST calls — no MCP server required.",
+  "author": {
+    "name": "Jason Stedwell"
+  },
+  "keywords": [
+    "memory",
+    "obsidian",
+    "notes",
+    "persistence",
+    "quicksilver"
+  ]
+}