runtime: fix PATH

[ConnorNelson]

Summary

• prepend stable challenge/workspace runtime paths to the image PATH
• derive /run/workspace/profile from the entrypoint path instead of passing PWN_WORKSPACE into containers
• expose /run/challenge/bin when /challenge/bin exists

Tests

• nix build .#pwn-workspace-runtime
• pwnshop run smoke check for PATH/profile links

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve .init-created challenge bins

Because linkChallengeBin() runs during setupRunDirectories() before .init is executed, /run/challenge/bin is never created when a challenge creates /challenge/bin from .init instead of shipping it in the image. For challenges based on the generic challenges/common/Dockerfile.j2, which does not itself add /challenge/bin back to the image PATH, those runtime-created tools were previously found through the hard-coded /challenge/bin entry but now remain unreachable for the whole session; create the symlink unconditionally or refresh it after runInit().

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