chore: add project configs, backend repair services, docs, and code quality tooling

- Add pre-commit hooks (ruff, black, prettier) and ESLint/Prettier configs
- Add backend repair services (execution, orchestration, preview) with tests
- Add project documentation (CLAUDE.md, README.md, design specs and plans)
- Add MissingTagsInlinePanel component for exception handling
- Add pyproject.toml with ruff/black configuration

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/pyproject.toml

@@ -0,0 +1,41 @@
+<![CDATA=[tool.ruff]
+line-length = 100
+target-version = "py311"
+
+exclude = [
+    ".git",
+    "__pycache__",
+    "build",
+    "dist",
+    ".venv",
+    "venv",
+    "migrations",
+]
+
+select = [
+    "E",   # pycodestyle errors
+    "W",   # pycodestyle warnings
+    "F",   # pyflakes
+    "I",   # isort
+    "C",   # flake8-comprehensions
+    "B",   # flake8-bugbear
+    "UP",  # pyupgrade
+    "RUF", # ruff-specific rules
+]
+
+ignore = [
+    "E501",  # line too long (handled by formatter)
+    "B008",  # do not perform function calls in argument defaults
+    "C901",  # too complex (handled separately)
+]
+
+[tool.ruff.format]
+quote-style = "single"
+indent-style = "space"
+skip-magic-trailing-comma = false
+line-ending = "lf"
+
+[tool.black]
+line-length = 100
+target-version = ['py311']
+]]>