chore(deps): add types-PyYAML to dev extras for mypy

[ptimizeroracle]

Unblocks the mypy failures on two in-flight branches.

mypy's ignore_missing_imports = true (already set in [tool.mypy]) suppresses
import-not-found but not import-untyped — the latter fires when stubs are
published on PyPI but not installed. Both in-flight branches trip it on import yaml:

Branch	PR	Error
wt/t35-unified	#180	ondine/mcp/server.py:31
wt/t6-plan	#181	ondine/orchestration/intent/planner.py:134

Landing the stub package here removes that error from both before they rebase,
rather than each branch fixing it independently and conflicting on pyproject.toml.

Verified locally on this branch:

• mypy ondine/ → Success: no issues found in 115 source files
• pytest tests/unit/ → 967 passed, 12 skipped

Note: uv.lock is regenerated (adds types-pyyaml 6.0.12.20260724). #180 and #182
also touch uv.lock and will need uv lock re-run after rebasing onto this — never
a hand-merge.

Summary by CodeRabbit

• Chores
  • Improved development tooling with enhanced type support for YAML configuration files.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: fa9eb1c6-61c7-4548-8f00-77eb4d6ce048

📥 Commits

Reviewing files that changed from the base of the PR and between cdc14f1 and e6d6268.

⛔ Files ignored due to path filters (1)

• uv.lock is excluded by !**/*.lock

📒 Files selected for processing (1)

• pyproject.toml

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📝 Walkthrough

Walkthrough

The development optional dependency group now includes types-PyYAML>=6.0.12 to provide YAML typing stubs.

Changes

YAML typing dependency

Layer / File(s)	Summary
Development dependency update pyproject.toml	Adds types-PyYAML>=6.0.12 to the development optional dependencies.

Estimated code review effort: 1 (Trivial) | ~2 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: adding types-PyYAML to dev extras to support mypy.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chore/mypy-yaml-stubs

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