fix: strip YAML comments before template rendering

[Hermsi1337]

Summary

Fixes #151.

The stack/services/volumes input is rendered as a Go text/template before it is parsed as YAML, so template expressions inside YAML comments were evaluated as well:

• A commented-out line such as # db_url: {{ .Env.DATABASE_URL }} failed the whole deployment with map has no entry for key "DATABASE_URL" (because of missingkey=error).
• Broken or partial template syntax inside a comment (# see {{) produced a misleading parse error pointing at the wrong line.

Changes

• cmd/action/main.go: new stripYamlComments() is called in loadYamlOptional() right before template.Parse. The scanner removes comments while preserving the line count (error messages keep pointing at the correct line) and knows the cases where # is not a comment:
  • inside single- and double-quoted scalars (including multi-line double-quoted scalars),
  • when not preceded by whitespace (image: nginx#latest),
  • inside block scalars (command: | followed by #!/bin/sh).
• cmd/action/main_test.go: 10 end-to-end regression tests plus a 14-case table test for stripYamlComments, including non-regression tests asserting that templating outside comments still works and that missingkey=error still fires there.
• README.md: note in the "Environment Variable Parsing" section that comments are stripped before rendering, so template expressions inside comments are inert.
• .gitattributes (separate commit): enforce LF line endings (* text=auto eol=lf) so Windows checkouts with core.autocrlf stay gofmt-clean.

Testing

• go test ./...: 49 tests pass (26 new).
• go vet ./...: clean.
• golangci-lint (the Makefile's quay.io/mittwald/golangci-lint:0.0.38 image): no findings.

Known limitation

The scanner tracks quote state conservatively: an apostrophe in an unquoted scalar (e.g. description: user's app) opens single-quote state, so comments until the next apostrophe are left in place. In that case behavior simply degrades to the status quo before this PR — legitimate content is never stripped.

🤖 Generated with Claude Code