feat: add artifact-driven SDLC workflow

[IchenDEV]

Change artifact

• Change: docs/sdlc/changes/2026-08-29-sdlc-bootstrap.md
• Accepted Intent/Spec evidence: user invocation of $ai-native-sdlc and explicit instruction to remove the legacy parallel workflow

Outcome

• Establishes docs/sdlc as the single lifecycle source for changes, incidents, and evals.
• Adds dependency-free contract checks, PR gating, and a ready-to-release gate for versioned macOS releases.
• Migrates the completed Plugin Hot Reload history and removes the obsolete docs/superpowers specs/plans tree.

Verification

• python3 -m unittest script/test_check_sdlc.py — 7 passed.
• python3 script/check_sdlc.py — contract valid.
• Release negative path rejects this verified change because it is not ready-to-release.
• Developer settings and plugin bridge tests — 4 passed, 46 assertions.
• Changed workflow YAML parses and git diff --check passes.
• No product UI changed; real-window visual QA is not applicable.
• Focused Rust Plugin Hot Reload tests are blocked before execution by the existing Ghostty/Zig 0.15.2 INFINITY compile error; this is recorded in the change artifact.

Review and release

• Risk level: medium — repository workflow and release gating change, no runtime product code change.
• Release target: none.
• Rollback: revert this PR to restore the prior repository workflow.
• The user explicitly authorized creating and merging this PR. This does not authorize a versioned product release.