Unify workflow scripts under a single Python implementation per command

[mnriem]

Goal

Replace the paired bash (.sh) + PowerShell (.ps1) scripts with one Python script per occurrence, eliminating dual-maintenance and the jq/manual-JSON divergence. The specify CLI is already Python, so the interpreter is guaranteed present — no new runtime dependency.

Scope

~4,500 lines across ~10 script pairs:

• Core scripts/{bash,powershell}/ — common, check-prerequisites, create-new-feature, setup-plan, setup-tasks
• extensions/agent-context/scripts/ — update-agent-context
• extensions/git/scripts/ — git-common, initialize-repo, auto-commit, create-new-feature-branch

Strategy

Incremental. Introduce py as a third script type alongside sh/ps, port one script end-to-end as a proof of concept with output-parity tests, then migrate the rest. Only after parity is proven do we consider deprecating sh/ps.

Contract to preserve

Agents parse script stdout (FEATURE_DIR:…, AVAILABLE_DOCS:…, JSON shapes, and the --json / --paths-only / --require-tasks / --include-tasks flags). Behavioral parity is the acceptance bar for every port.

Sub-issues

• Fix/extension hooks not triggered #1 — Add py script type & interpreter resolution (foundation)
• docs: Add Extensions & Presets section to README #2 — PoC: port check-prerequisites to Python + parity tests (depends on Fix/extension hooks not triggered #1)
• Add AIDE, Extensify, and Presetify to community extensions #3 — Port core common + create-new-feature + setup-plan + setup-tasks (depends on docs: Add Extensions & Presets section to README #2)
• chore: use PEP 440 .dev0 versions on main after releases #4 — Port agent-context extension scripts (depends on docs: Add Extensions & Presets section to README #2)
• docs: streamline install section and add community overview #5 — Port git extension scripts (depends on docs: Add Extensions & Presets section to README #2)
• Improve docs site color scheme for better contrast #6 — Update templates' scripts: frontmatter to add py: lines (depends on Add AIDE, Extensify, and Presetify to community extensions #3–docs: streamline install section and add community overview #5)
• docs: strengthen agent disclosure to cover commits and per-round comments #7 — Docs, AGENTS.md, and migration/deprecation plan (depends on Improve docs site color scheme for better contrast #6)

(Sub-issue numbers to be filled in once the linked issues are created.)

Out of scope (for now)

Removing .sh/.ps1 files. They stay until py reaches full parity and adoption.

[mnriem]

Recreated in upstream github/spec-kit (github#3277 and sub-issues). Closing fork duplicate.