[task] Add shellcheck disable directives for markdown heredoc false positives

[github-actions]

Objective

Add shellcheck disable directives to heredoc blocks in compiled workflows to suppress 945 false positive warnings (SC2006/SC2287) caused by markdown backticks in prompt documentation.

Context

Static analysis scan identified 945 false positives from shellcheck misinterpreting markdown backticks (e.g., /tmp/gh-aw/agent/) in heredoc documentation as command substitution. These are not actual security issues but create noise in linting output.

Related to discussion #3527.

Approach

Apply the fix template from /tmp/gh-aw/cache-memory/fix-templates/actionlint-sc2006-sc2287-heredoc-backticks.md:

1. Identify heredoc blocks in workflow compilation code that write markdown with backticks
2. Add shellcheck disable comment above affected heredoc blocks:

   # shellcheck disable=SC2006,SC2287
   cat >> "$GH_AW_PROMPT" << PROMPT_EOF
   ...markdown content with backticks...
   PROMPT_EOF

3. This should be done in the Go compiler code that generates the prompt writing step

Files to Modify

• pkg/workflow/compiler.go or related workflow generation files where heredoc prompt writing is generated
• Any other workflow compilation code that generates heredoc blocks with markdown content

Acceptance Criteria

• Shellcheck disable directives added to heredoc generation in compiler
• Recompile workflows with make recompile
• Re-run gh aw compile --actionlint shows reduced findings (945 fewer warnings)
• Verify compiled .lock.yml files contain disable directives
• No functional changes to workflow execution

Impact

Reduces linting findings from 953 to 8 (99.2% reduction), making actionlint output more useful for identifying real issues.
Related to #3527

AI generated by Plan Command for discussion #3527