Add content-type input with smart auto-detection

- Add `content-type` input to override auto-detected content type
- Include `unspecified` as a valid value (matches backend/frontend)
- Rewrite `determineContentType` to verify file contents against
  extensions using magic bytes: gzip header (1f 8b), tar header
  (ustar at offset 257), and decompressed tar-inside-gzip check
- Warn when extension doesn't match actual file contents
- Fall back to content-based heuristics when no extension matches

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

Author: jason-rl

action.yml

@@ -56,6 +56,10 @@ inputs:
     description: 'Path to file or tar archive (required if source-type=tar/file)'
     required: false
 
+  content-type:
+    description: 'Object content type override (unspecified, text, binary, gzip, tar, tgz). If omitted, auto-detected from file extension and magic bytes.'
+    required: false
+
   # Common inputs
   setup-commands:
     description: 'Newline-separated setup commands to run after agent installation'

dist/index.js

@@ -126,7 +126,7 @@ async function deployTarAgent(
   const tarPath = resolvePath(inputs.path);
 
   // Upload tar file
-  const uploadResult = await uploadTarFile(client, tarPath, inputs.objectTtlDays, inputs.isPublic);
+  const uploadResult = await uploadTarFile(client, tarPath, inputs.objectTtlDays, inputs.isPublic, inputs.contentType);
 
   // Create agent with object source
   // Using client.api.post because SDK v1.0.0 types are missing 'version' field in AgentCreateParams
@@ -173,7 +173,8 @@ async function deployFileAgent(
     client,
     filePath,
     inputs.objectTtlDays,
-    inputs.isPublic
+    inputs.isPublic,
+    inputs.contentType,
   );
 
   // Create agent with object source