chore: bump CLI version 0.1.0 → 0.5.0 + introduce CHANGELOG

[ashmitb95]

Summary

Catches __version__ up to ~6 months of shipped milestones. The constant in src/canopy/__init__.py never moved while M0/M1/M2/M3/M4/M5 + Wave 2.3 shipped — meaning the doctor's cli_stale / mcp_stale checks (M1) had nothing real to compare against. Found while running docs/test-plan.md §0 against canopy-test: canopy --version reported 0.1.0 even though the M3 + M4 surface was clearly working.

Changes

• src/canopy/__init__.py: 0.1.0 → 0.5.0. Aligns with the latest core milestone (M5); stays pre-1.0 because end-to-end validation is what we're doing now.
• CHANGELOG.md (new at repo root): captures the 0.1.0 → 0.5.0 jump in one section. Going forward, each milestone PR adds its own section. The VSCode extension already has its own changelog at vscode-extension/CHANGELOG.md — this is the Python side.
• CLAUDE.md: one-liner under "Important Implementation Details" reminding future-us to bump __version__ + CHANGELOG when shipping a milestone. Prevents the same drift from recurring.

Verification

After pip install -e .:

$ canopy --version
canopy 0.5.0

$ python -c "from canopy.mcp.server import version; import json; print(json.dumps(version()))"
{"cli_version": "0.5.0", "mcp_version": "0.5.0", "schema_version": "1"}

After merge

• Reinstall locally: pip install -e . (or pipx reinstall canopy).
• Resume docs/test-plan.md execution from §0 with the correct version reported.