build(deps): bump and align black, ruff versions

Bump black 26.3.1→26.5.1 and ruff 0.6.0→0.15.20 in pyproject.toml.
Unpin black (== → >=) to match ruff convention.
Sync .pre-commit-config.yaml revs to match.
Drop default_language_version — hooks work on any Python ≥3.10.
Document dual-config pattern in AGENTS.md to prevent future drift.

.pre-commit-config.yaml

@@ -1,15 +1,12 @@
-default_language_version:
-  python: python3.13
-
 repos:
   - repo: https://github.com/psf/black
-    rev: 25.11.0
+    rev: 26.5.1
     hooks:
       - id: black
         files: ^pandas_ta_classic/
 
   - repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: v0.14.13
+    rev: v0.15.20
     hooks:
       - id: ruff
         args: [--select, "E9,F63,F7,F82"]

AGENTS.md

@@ -131,6 +131,7 @@ After each coding session, execute the code/module in local venv and troubleshoo
 - Config in `pyproject.toml` under `[tool.black]` and `[tool.ruff]`
 - If black and ruff format disagree on a region, lock it with `# fmt: off` / `# fmt: on`
 - **Gate condition:** `black --check --diff pandas_ta_classic/` and `ruff check pandas_ta_classic --select E9,F63,F7,F82` must both return EXIT=0 before the task is considered complete. If black reports a reformat, run `black pandas_ta_classic/` then re-check.
+- **Dual config pattern:** black/ruff versions appear in two places — `pyproject.toml` under `[project.optional-dependencies].lint` (CI installs via `pip install -e ".[lint]"`) AND `.pre-commit-config.yaml` under each hook's `rev`. When bumping a version, update BOTH. Versions must be kept in sync.
 
 ## Imports and Paths
 

pyproject.toml

@@ -59,8 +59,8 @@ oracle = [
 
 # CI code quality tools
 lint = [
-    "ruff>=0.6.0",
-    "black==26.3.1",
+    "ruff>=0.15.20",
+    "black>=26.5.1",
 ]
 
 # PyPI publishing tools