Mcpb env file arg (#694)

* fix: mcpb bundles pass --env.file so the default credential store is created

Completes #692: the engine creates/sources the env file only when --env.file
is set, and the bundle manifest never passed it, so packaged installs got no
placeholder and reload_credentials had nothing to source. ${HOME} as a plain
arg, same Windows-backslash constraint as --approot.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix: same --env.file arg in the multiplatform bundle manifest

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: jeffreyaven

packaging/mcpb/manifest/manifest.combined.template.json

@@ -26,6 +26,8 @@
         "--mcp.server.type=stdio",
         "--approot",
         "${HOME}/.stackql",
+        "--env.file",
+        "${HOME}/.stackql/.env",
         "--mcp.config",
         "{\"server\": {\"audit\": {\"disabled\": true}}}"
       ],

packaging/mcpb/manifest/manifest.template.json

@@ -26,6 +26,8 @@
         "--mcp.server.type=stdio",
         "--approot",
         "${HOME}/.stackql",
+        "--env.file",
+        "${HOME}/.stackql/.env",
         "--mcp.config",
         "{\"server\": {\"audit\": {\"disabled\": true}}}"
       ]