docs: add comprehensive DevContainer maintenance and improvement plan

- HIGH PRIORITY openai#1: File structure refactoring (group by component type)
- Target structure: statestore/, pubsub/, bindings/, secretstore/, configuration/
- Removes redundant prefixes from YAML filenames
- 13 total items categorized by priority (HIGH/MEDIUM/LOW)
- Includes effort estimates (35-45 hours total) and phased approach
- Quick wins section for immediate value (2.5 hours)
- All items tracked via manage_todo_list for traceability

Rationale: Proper directory organization improves maintainability,
follows coding methodology, and makes adding new components easier.

Author: DeanLuus22021994