fix(release): mark main as v0.6 development

[stacknil]

Summary

• Set CMake's numeric project version to 0.6.0 and add a default -dev prerelease suffix.
• Compile the composed 0.6.0-dev value into the CLI and pin it in the CLI regression test.

Why

main already contains the unreleased v0.6 episode semantics, finding identity, and audit signals, but loglens --version still reported the published v0.5.0 release.

How to validate

• cmake -S . -B build -DBUILD_TESTING=ON
• cmake --build build --config Release
• ctest --test-dir build -C Release --output-on-failure
• loglens --version prints LogLens 0.6.0-dev
• Repeated with GCC under WSL; 6/6 tests passed on both toolchains.

Risk / rollout notes

• Design decision: keep CMake's project version numeric while composing the SemVer prerelease suffix separately, so RC and stable builds can use -rc1 and an empty suffix.
• Main risk: downstream scripts that asserted the stale 0.5.0 CLI output will need to accept the correct development version.
• Compatibility impact: no parser, detector, report, or CLI argument behavior changes; only version reporting changes.
• Rollback path: revert commit 1e28b66 to restore the previous CMake and CLI version.

[stacknil]

Post-CI diff review complete.

• Design decision: keep CMake's project version numeric at 0.6.0 and compose the -dev prerelease suffix for the CLI, leaving a direct path to -rc1 and stable builds.
• Main risk: scripts asserting the stale v0.5.0 version output will see the intentional development version.
• Compatibility impact: parser, detector, report, and CLI argument behavior are unchanged; version reporting only.
• Rollback path: revert 1e28b66.

Ubuntu, Windows, fuzz, Repo Sentinel, and CodeQL checks passed; the remote diff is limited to two expected files and git diff --check is clean. No bot or reviewer comments were present.