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/meta_plugin/read_time.rs

@@ -97,8 +97,10 @@ impl MetaPlugin for ReadTimeMetaPlugin {
         self.base.outputs()
     }
 
-    fn outputs_mut(&mut self) -> &mut std::collections::HashMap<String, serde_yaml::Value> {
-        self.base.outputs_mut()
+    fn outputs_mut(
+        &mut self,
+    ) -> anyhow::Result<&mut std::collections::HashMap<String, serde_yaml::Value>> {
+        Ok(self.base.outputs_mut())
     }
 
     fn default_outputs(&self) -> Vec<String> {
@@ -109,8 +111,10 @@ impl MetaPlugin for ReadTimeMetaPlugin {
         self.base.options()
     }
 
-    fn options_mut(&mut self) -> &mut std::collections::HashMap<String, serde_yaml::Value> {
-        self.base.options_mut()
+    fn options_mut(
+        &mut self,
+    ) -> anyhow::Result<&mut std::collections::HashMap<String, serde_yaml::Value>> {
+        Ok(self.base.options_mut())
     }
 }
 use crate::meta_plugin::register_meta_plugin;