feat: allow custom specs directory via --specs-dir; default to specs/

[gotalab]

Summary

• Adds --specs-dir to specify init and saves it to git config (spec-kit.specsDir).
• Scripts resolve the specs base directory from git config; default remains specs/.

Motivation

• Make it easier to align with project documentation structures (e.g., docs/specs) while keeping backwards compatibility.

Changes

• src/specify_cli/init.py: add --specs-dir to init; persist to git config when repo exists.
• scripts/common.sh: get_feature_dir() reads spec-kit.specsDir (fallback to specs).
• scripts/update-agent-context.sh: FEATURE_DIR resolves via spec-kit.specsDir.
• scripts/create-new-feature.sh: SPECS_DIR resolves via spec-kit.specsDir.
• README.md: minimal usage examples and optional post-copy note.

Usage

• New: uvx --from git+https://github.com/github/spec-kit.git specify init my-app --specs-dir docs/specs
• Here: specify init --here --specs-dir tmp/specs

Compatibility

• No breaking changes; defaults to specs/ if unset.

Testing

• Verified end-to-end with the Spec-Driven Development workflow on Claude Code, Gemini CLI and GitHub Copilot
• To test script functionality, the following command executed:

uvx --from path/to/spec-kit/ specify init --here --specs-dir docs/specs \
&& rsync -a --delete path/to/spec-kit/scripts/ ./scripts/ \
&& chmod +x ./scripts/*.sh

[peterHoburg]

IMO it should be .speckit . Many tools are using . dirs now.
.claude .cursor .github .venv .agent-os etc...

Related to #38

[mkellerman]

Please see my implementation here: #86

[gotalab]

I agree. .speckit feels consistent with the other tools.
Close this PR.