Fix stale AWS/Bedrock auth carrying over on backend switch

When a project switched backends (e.g. Bedrock -> Anthropic), the
recreated container kept authenticating against Bedrock, and SSO kept
firing after switching away. Three root causes, all fixed:

1. Recreation builds the new container from a `docker commit` snapshot.
   commit always bakes the previous container's full ENV into the image
   (an empty commit Config does NOT strip it, and the commit API cannot
   remove env). So CLAUDE_CODE_USE_BEDROCK=1 / AWS_* survived into the
   new container. Fix: create_container now explicitly clears every
   managed auth key the active backend does not set (MANAGED_AUTH_KEYS),
   so create-time env overrides the stale baked-in values.

2. awsAuthRefresh was written into ~/.claude.json (persisted home
   volume) and never removed, so Claude Code kept invoking
   triple-c-sso-refresh after switching to a non-SSO backend. Fix:
   entrypoint now deletes awsAuthRefresh when AWS_SSO_AUTH_REFRESH_CMD
   is unset, idempotent both ways.

3. Static/session AWS creds were baked into Config.Env at create time,
   so a stop/start kept stale creds and rotated keys never refreshed
   without a full recreation. Fix: static creds are no longer injected
   as env vars; write_bedrock_static_credentials() writes
   ~/.aws/credentials (0600, secrets via exec env not argv) on every
   start, and removes a stale ~/.aws/config left from a prior profile/SSO
   session. Static creds also dropped from the bedrock fingerprint so a
   key rotation refreshes in place instead of forcing recreation.

Adds exec_oneshot_env() for env-carrying one-shot execs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src-tauri/src/commands/project_commands.rs

@@ -432,6 +432,13 @@ pub async fn start_project_container(
             new_id
         };
 
+        // Refresh Bedrock static/session credentials on every start so rotated
+        // keys are picked up without a full container recreation. No-op for
+        // other backends / auth methods.
+        if let Err(e) = docker::write_bedrock_static_credentials(&container_id, &project).await {
+            log::warn!("Failed to refresh AWS credentials for project {}: {}", project.id, e);
+        }
+
         Ok(container_id)
     }.await;