feat(devcontainer): add init-home.sh for PVC bootstrap

Links cargo binaries, creates sccache dir, and writes default .zshrc
on first boot. No-op on subsequent sessions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.devcontainer/init-home.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+set -euo pipefail
+
+# Bootstrap cargo into PVC-backed home if not already present
+if [ ! -d "$HOME/.cargo/bin" ]; then
+    echo "[init-home] First run: linking cargo toolchain..."
+    mkdir -p "$HOME/.cargo/bin"
+    # Copy cargo config and link binaries from shared rustup
+    for bin in /opt/cargo/bin/*; do
+        ln -sf "$bin" "$HOME/.cargo/bin/$(basename "$bin")"
+    done
+    echo "[init-home] Cargo toolchain linked."
+fi
+
+# Ensure sccache cache dir exists
+mkdir -p "${SCCACHE_DIR:-$HOME/.cache/sccache}"
+
+# Default .zshrc if none exists (oh-my-zsh is in the image, config in PVC)
+if [ ! -f "$HOME/.zshrc" ]; then
+    cp /home/dev/.oh-my-zsh/templates/zshrc.zsh-template "$HOME/.zshrc" 2>/dev/null || true
+    echo 'export PATH="$HOME/.cargo/bin:$PATH"' >> "$HOME/.zshrc"
+    echo 'export SQLX_OFFLINE=true' >> "$HOME/.zshrc"
+fi
+
+echo "[init-home] Ready."