fix(homebrew): Set executable permissions before generating completions

[philprime]

Set executable permissions on the installed Apple Docs binary before generating shell completions, fixing Homebrew's EACCES failure for raw downloads with mode 0644. Publish v0.0.5 as revision 1 while preserving the existing v0.0.4 revision and leaving future releases at revision 0.

Add a regression test that installs a non-executable fixture and verifies Bash, Zsh, and Fish completion generation across all configured platforms.

Validation

• make test-homebrew passes, with the new regression test confirmed failing before the fix.
• The updated formula installs the actual v0.0.5 macOS ARM64 download and generates all three completion scripts in an isolated temporary prefix.
• Homebrew style, formatting, and pre-commit checks pass.
• Full make test is blocked locally by missing rpmbuild. The publisher configuration-only check passes.

Publication
After merge, rerun publish.yml with source_repo=techprimate/apple-docs-cli and tag=v0.0.5 to publish the formula revision through the automated tap PR. No release binaries or checksums change.