Merge the v0.8.6 feature batch and release hardening.\n\nIncludes the full #373-#380/#382-#402 milestone scope, version bump to 0.8.6, secure /share temp-file handling, Windows-safe self-update replacement, and CI portability fixes.\n\nRemote PR checks passed on the final head before merge.
- Move src/* into crates/tui/src/ to create a proper workspace structure
- Add .claude/ and .trimtab/ directories for Trimtab closed-loop workflow
- Add DEPENDENCY_GRAPH.md and update documentation
- Update Cargo.toml files to reflect new crate dependencies
- Update CI workflows and npm package scripts
- All tests pass, release build works
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