feat: structured dead-code detection pipeline with multi-mode output

[nextlevelshit]

Summary

• Rewrote the dead-code detection pipeline into a family of 4 pipelines: scan-only (dead-code.yaml), PR comment (dead-code-pr.yaml), GitHub issue (dead-code-issue.yaml), and heal (dead-code-heal.yaml)
• Expanded the dead-code-scan.schema.json contract with new detection categories (duplicate, stale_glue, hardcoded_value), line range support, and suggested actions
• Added three new output contract schemas: dead-code-report, dead-code-pr-result, and dead-code-issue-result
• Extended the github-commenter persona permissions in wave.yaml to support PR commenting
• Added comprehensive unit tests for schema validation and pipeline YAML parsing

Closes #135

Changes

• .wave/contracts/dead-code-scan.schema.json — Expanded with new categories, line_range, suggested_action fields
• .wave/contracts/dead-code-report.schema.json — New schema for formatted markdown report output
• .wave/contracts/dead-code-pr-result.schema.json — New schema for PR comment posting result
• .wave/contracts/dead-code-issue-result.schema.json — New schema for GitHub issue creation result
• .wave/pipelines/dead-code.yaml — Rewritten as scan-only + local format pipeline (removed clean/verify/create-pr steps)
• .wave/pipelines/dead-code-pr.yaml — New pipeline: scan + format + publish PR comment
• .wave/pipelines/dead-code-issue.yaml — New pipeline: scan + format + create GitHub issue
• .wave/pipelines/dead-code-heal.yaml — New pipeline: extracted heal flow from original dead-code pipeline
• wave.yaml — Extended github-commenter persona with gh pr comment* permission
• internal/contract/dead_code_schemas_test.go — Schema validation tests for all contract schemas
• internal/pipeline/dead_code_pipelines_test.go — Pipeline YAML parse and dependency resolution tests
• specs/135-dead-code-pipeline/ — Spec, plan, and task artifacts

Test Plan

• Schema validation tests cover all new categories (duplicate, stale_glue, hardcoded_value), new fields (line_range, suggested_action), and backward compatibility with existing payloads
• Pipeline YAML parse tests verify all 4 pipelines load correctly, resolve step dependencies, and reference valid personas
• All tests located in internal/contract/ and internal/pipeline/ packages

[nextlevelshit]

Code Review (Wave Pipeline)

Verdict: REQUEST_CHANGES

Blocking Issues

1. Missing BasicProgressDisplay guard test — both reviewers flagged this independently, confirming it's a real coverage gap
2. Silent observability regression from unstaged executor.go change — artifact injection messages are dropped in CI/non-TTY output

Non-Blocking Improvements

Four non-blocking improvements were also surfaced:

• Test safety with t.Chdir
• Fragile timeouts
• PipelineID inconsistency
• State tracking type inconsistency

Positive Observations

Overall quality of the committed fix was noted positively by both reviewers.

Assessment

The implementation is too shallow and too destructive; may need full re-implementation.

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