fix: harden security, eliminate panics, remove dead code, add Dockerfile

Security:
- Use constant-time password comparison (subtle crate) to prevent timing attacks
- Replace permissive CORS with configurable origin-restricted CORS
- Add TLS warning when password auth is used without HTTPS

Bug fixes:
- Convert MetaPlugin panics to anyhow::Result (get_meta_plugin, outputs_mut, options_mut)
- Replace item.id.unwrap() with proper error handling across 15 call sites
- Fix panic on unknown column type in list mode
- Fix conflicting PIPESIZE constant (was 8192 vs 65536, now unified to 8192)
- Add 256MB filter chain buffer limit to prevent OOM
- Gracefully skip unregistered plugins instead of panicking

Dead code removal:
- Delete unused filter parser files (filter_parser.rs, filter.pest, parser/ module)
- ~260 lines of dead PEG parser code removed

Code consolidation:
- Add is_content_binary_from_metadata() helper (was duplicated in 4 places)
- Simplify save_item_raw() to delegate to save_item_raw_streaming() (~90 lines removed)

Incomplete features:
- Populate filter_plugins in status output from global registry
- Add FallbackMagicFileMetaPlugin (was referenced but never implemented)
- Document init_plugins() as intentional no-op

Infrastructure:
- Add Dockerfile (static musl binary on scratch, 4.8MB)
- Add .dockerignore
- Add cors_origin to ServerConfig and config.rs

src/modes/common.rs

@@ -206,12 +206,14 @@ pub fn settings_meta_plugin_types(
             // Try to find the MetaPluginType by meta name
             let mut found = false;
             for meta_plugin_type in MetaPluginType::iter() {
-                let meta_plugin =
-                    crate::meta_plugin::get_meta_plugin(meta_plugin_type.clone(), None, None);
-                if meta_plugin.meta_type().to_string() == trimmed_name {
-                    meta_plugin_types.push(meta_plugin_type);
-                    found = true;
-                    break;
+                if let Ok(meta_plugin) =
+                    crate::meta_plugin::get_meta_plugin(meta_plugin_type.clone(), None, None)
+                {
+                    if meta_plugin.meta_type().to_string() == trimmed_name {
+                        meta_plugin_types.push(meta_plugin_type);
+                        found = true;
+                        break;
+                    }
                 }
             }