chore(claude): pin PQL_VAULT per project so cwd stops choosing the vault

pql is now a bare word on PATH, which removed the long incantation that had
been forcing --vault into every call by habit. Convenience lowered the cost
of the wrong thing without lowering the cost of the right one: a three-word
pql ticket new targets whichever vault the cwd happens to sit in, and there
are nine of them with colliding id sequences.

PQL_VAULT in each project settings file makes the vault a property of the
session rather than of the working directory — the same lesson Rule 3 records
for git -C, applied to pql. Verified the env var overrides cwd discovery,
that an explicit --vault still beats the env var, and that the harness
hot-reloads it without a restart.

This does not make provenance visible: no output says which vault answered,
so a forgotten --vault still returns a well-formed answer about the wrong
dataset. That remains T-37.

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

.claude/settings.json

@@ -1,4 +1,7 @@
 {
+  "env": {
+    "PQL_VAULT": "/mnt/media/Projects/core-api"
+  },
   "permissions": {
     "allow": [
       "Bash(pql)",