fix(discover): report Windows sessions instead of always zero

[make0uthill]

Summary

On Windows, rtk discover and rtk session report 0 commands even for projects with a long transcript history. Two independent causes in the Claude transcript provider, both fixed here:

• encode_project_path left the drive-letter colon intact, producing D:-Code-... while Claude Code writes D--Code-... on disk. : is not a legal character in a Windows directory name, so the slug it creates cannot contain one — every lookup missed.
• The tool_use scan matched only "Bash" blocks. On Windows the agent issues most commands through the PowerShell tool, so the bulk of the transcript was skipped even once the directory was found.

test_encode_project_path_windows asserted the buggy slug (C:-Users-foo-bar), so it is updated to the value that actually appears on disk.

Test plan

• cargo fmt --all && cargo clippy --all-targets && cargo test — 2554 passed, 0 failed
• Manual testing: on a real project directory rtk discover went from 0 sessions to 278 commands across 10 sessions, with the reported rewrites matching what the hook actually does.

Targets develop as required.

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