chore(zed): pin rust-analyzer for firmware crate

Zed's bundled rust-analyzer calls `cargo metadata --lockfile-path`,
which is still gated behind `-Z unstable-options` on cargo 1.95.0
(both stable and the esp Xtensa fork). Workspaces fail to load with
the bundled binary.

Point lsp.rust-analyzer.binary.path at the rustup-managed
rust-analyzer (version-locked to cargo 1.95 stable, no unstable
flags). Also set cargo.target = xtensa-esp32s3-espidf with
allTargets=false so RA doesn't try to check the crate for the host
target — esp-idf-sys can't build for macOS.

.zed/settings.json

@@ -1,4 +1,21 @@
 {
+  "lsp": {
+    "rust-analyzer": {
+      "binary": {
+        "path": "/Users/julien/.rustup/toolchains/stable-aarch64-apple-darwin/bin/rust-analyzer",
+        "arguments": []
+      },
+      "initialization_options": {
+        "cargo": {
+          "target": "xtensa-esp32s3-espidf",
+          "allTargets": false
+        },
+        "check": {
+          "allTargets": false
+        }
+      }
+    }
+  },
   "languages": {
     "JavaScript": {
       "formatter": { "language_server": { "name": "oxc" } },