feat: Add Claude Code agent skills for Feast (#6081)

* feat: add Claude Code agent skills for Feast

Add two agent skills following the anthropics/skills SKILL.md format:

- feast-dev: Development guide for contributors covering setup, testing,
  linting, code style, project structure, and key abstractions
- feast-feature-engineering: User-facing guide for building feature stores
  covering feature definitions, materialization, online/offline retrieval,
  on-demand transformations, and CLI reference

Closes #5976

Signed-off-by: Sagar Gupta <sg85207@gmail.com>

* refactor: move skills to top-level dir, add Agent Skills spec compatibility

- Move from .claude/skills/ to skills/ for platform-agnostic placement
- Add license, compatibility, and metadata fields per agentskills.io spec
- Skills now work with Claude Code, OpenAI Codex, and any Agent Skills
  compatible tool

Addresses feedback from @franciscojavierarceo regarding OpenAI compatibility.

Signed-off-by: Sagar Gupta <sg85207@gmail.com>

* refactor: scope to dev/contributor skill only

Remove feast-feature-engineering skill to avoid overlap with #6007
which covers user-facing content more comprehensively. This PR now
focuses exclusively on the developer/contributor workflow skill.

Signed-off-by: Sagar Gupta <sg85207@gmail.com>

* fix: align commands with Makefile and CLAUDE.md

Address Devin Review findings:
- Use make install-python-dependencies-dev instead of uv pip install
- Remove nonexistent start-local-integration-tests target
- Fix type-check command to cd sdk/python && python -m mypy feast
- Add make test-python-unit-fast and make precommit-check targets

Signed-off-by: Sagar Gupta <sg85207@gmail.com>

* fix: correct test file path to test_unit_feature_store.py

Address Devin Review finding: the example pytest commands referenced
test_feature_store.py which doesn't exist. The actual file is
test_unit_feature_store.py. Also use -k flag for test name filtering
instead of :: class notation.

Signed-off-by: Sagar Gupta <sg85207@gmail.com>

* fix: correct CLI entry point path to cli/cli.py

Signed-off-by: Sagar Gupta <sg85207@gmail.com>

---------

Signed-off-by: Sagar Gupta <sg85207@gmail.com>

Author: Sagargupta16

skills/feast-dev/SKILL.md

@@ -0,0 +1,100 @@
+---
+name: feast-dev
+description: Development guide for contributing to the Feast codebase. Covers environment setup, testing, linting, project structure, and PR workflow for feast-dev/feast.
+license: Apache-2.0
+compatibility: Works with Claude Code, OpenAI Codex, and any Agent Skills compatible tool. Requires Python 3.10+, uv, and git.
+metadata:
+  author: feast-dev
+  version: "1.0"
+---
+
+# Feast Development Guide
+
+## Environment Setup
+
+```bash
+# Install development dependencies (uses uv pip sync with pinned requirements)
+make install-python-dependencies-dev
+
+# Install minimal dependencies
+make install-python-dependencies-minimal
+
+# Install pre-commit hooks (runs formatters and linters on commit)
+make install-precommit
+```
+
+## Running Tests
+
+### Unit Tests
+```bash
+# Run all unit tests
+make test-python-unit
+
+# Run a specific test file
+python -m pytest sdk/python/tests/unit/test_unit_feature_store.py -v
+
+# Run a specific test by name
+python -m pytest sdk/python/tests/unit/test_unit_feature_store.py -k "test_apply" -v
+
+# Run fast unit tests only (no external dependencies)
+make test-python-unit-fast
+```
+
+### Integration Tests (local)
+```bash
+# Run integration tests in local dev mode
+make test-python-integration-local
+```
+
+## Linting and Formatting
+
+```bash
+# Format Python code
+make format-python
+
+# Lint Python code
+make lint-python
+
+# Run all precommit checks (format + lint)
+make precommit-check
+
+# Type checking
+cd sdk/python && python -m mypy feast
+```
+
+## Code Style
+
+- Use type hints on all function signatures
+- Use `from __future__ import annotations` at the top of new files
+- Follow existing patterns in the module you are modifying
+- PR titles must follow semantic conventions: `feat:`, `fix:`, `ci:`, `chore:`, `docs:`
+- Add a GitHub label to PRs (e.g. `kind/bug`, `kind/feature`, `kind/housekeeping`)
+- Sign off commits with `git commit -s` (DCO requirement)
+
+## Project Structure
+
+```
+sdk/python/feast/          # Main Python SDK
+  cli/cli.py               # CLI entry point (feast apply, feast materialize, etc.)
+  feature_store.py         # FeatureStore class - core orchestration
+  repo_config.py           # feature_store.yaml configuration parsing
+  repo_operations.py       # feast apply / feast teardown logic
+  infra/                   # Online/offline store implementations
+    online_stores/         # Redis, DynamoDB, SQLite, etc.
+    offline_stores/        # BigQuery, Snowflake, File, etc.
+  transformation/          # On-demand and streaming transformations
+protos/feast/              # Protobuf definitions
+sdk/python/tests/          # Test suite
+  unit/                    # Fast, no external deps
+  integration/             # Requires infrastructure
+```
+
+## Key Abstractions
+
+- **FeatureStore** (`feature_store.py`): Entry point for all operations
+- **FeatureView**: Defines a set of features from a data source
+- **OnDemandFeatureView**: Computed features using request-time transformations
+- **Entity**: Join key definition (e.g. driver_id, customer_id)
+- **DataSource**: Where raw data lives (BigQuery, files, Snowflake, etc.)
+- **OnlineStore**: Low-latency feature serving (Redis, DynamoDB, SQLite)
+- **OfflineStore**: Historical feature retrieval (BigQuery, Snowflake, file)