docs(skills): add agent skills for simple_module_python

[antosubash]

Summary

Adds six standalone agent skills under skills/ (Anthropic Agent Skills format) so AI agents — Claude Code, Cursor, Codex, Windsurf, OpenCode, etc. — working in any simple_module_python project get the framework's invariants and workflows loaded into context on demand.

Publishable to skills.sh via:

npx skills add antosubash/simple_module_python

What's in the directory

Skill	Use when
simple-module-creating	Scaffolding a new module — entry-point, ModuleMeta, post-scaffold steps
simple-module-conventions	Writing/reviewing module code — SQLModel-everywhere, settings layout, framework→plugin direction, Zod-in-hooks, locale rules
simple-module-database	SQLModel tables, per-module Base, mixins, get_db lifecycle, no-session.commit()-in-services
simple-module-migrations	Alembic in the host, branch_labels on first revision, autogenerate covering installed modules
simple-module-inertia-pages	Render-key → file mapping, shared props (auth.user principal_serializer requirement), SM003/SM004/SM018
simple-module-doctor	Full SM001–SM018 reference table with fix per code

Design

• Standalone-friendly. No skill references paths internal to this dev repo (modules/, docs/, scripts/, packages/ui/, make targets). They install cleanly into a host project scaffolded with sm create-host or a module package scaffolded with sm create-module.
• Canonical CLI. Skills point at sm create-module, sm host gen-pages, and uv run alembic … directly rather than this repo's Makefile shortcuts.
• Description hygiene. Frontmatter description fields are "use when…" trigger phrases only — no workflow summaries. Per writing-skills guidance, summarized descriptions cause agents to follow the description in lieu of reading the body.
• Word counts. All six SKILL.md files are 559–673 words (vs. typical 1000+ on skills.sh), keeping context-window cost low when an agent loads multiple at once.

Verifying claims

Spot-checked against the codebase before landing:

• app.state.<module_lower> (no _settings suffix) — confirmed in modules/users/, modules/file_storage/, modules/background_tasks/. The diagnostics check accepts either lowercase package name or meta.name.lower().
• sm host gen-pages — confirmed as the canonical CLI form (plugin subcommand under the host group).
• ModuleMeta fields, mixin behavior, render-key mapping, branch-label requirement — verified against framework/core/, framework/db/, framework/hosting/.
• Diagnostic codes SM001, SM003, SM004, SM007–SM018 exist; SM002, SM005, SM006 are reserved/retired (called out in the doctor skill).

Publishing

After merge, the skills are reachable at github.com/antosubash/simple_module_python/tree/main/skills and discoverable via npx skills add antosubash/simple_module_python. To seed the leaderboard telemetry, run that command once locally.

Test plan

• Manually install in a clean directory: npx skills add antosubash/simple_module_python --list lists all six.
• Install one skill into Claude Code: npx skills add antosubash/simple_module_python --skill simple-module-creating -a claude-code — verify .claude/skills/simple-module-creating/SKILL.md appears.
• Skim each SKILL.md — confirm no make/scripts//modules/products//docs/ references to repo-internal paths.
• Confirm npx skills add antosubash/simple_module_python --skill '*' -a claude-code installs all six.