Add automatic project memory

[khang859]

Summary

• add Claude Code-style automatic project memory stored locally under ~/.rune/projects//memory/MEMORY.md
• inject saved project memory as non-authoritative <auto_memory> context each turn
• extract memory updates in the TUI after idle turn completion, with /memory controls and settings integration
• add redaction/safety filters and tests for storage, extraction, settings, and TUI edge cases

Validation

• GOTOOLCHAIN=go1.26.0 go test ./internal/config ./internal/memory ./internal/agent ./internal/tui/modal ./internal/tui