feat(skills): add coding-dev.md and per-language rules under code-languages/

Generic coding rules and preferences distilled from existing agent rule
files, project AGENTS.md/.rules, and saved memories:

- strictness maximal; suppressions must be reported to the user
- never filter build/lint/test output through grep/tail/head
- reuse > fork > self-implement; generic code becomes its own package
- 1000-line file / 100-line function limits, split by concern
- regression test every fixed bug; never test against real user data
- events over polling; scope discipline; honest reporting

Per-language: rust, js-typescript, bash, python, go, csharp-dotnet, c-cpp.
Each extends coding-dev.md rather than repeating it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -6,7 +6,36 @@ A collection of public, reusable agent skills, cheatsheets, and operational work
 
 ## 📂 Skills Index
 
-*(Public skills will be added here as generic, open workflows)*
+| Skill File | Scope / Topics Covered |
+| :--- | :--- |
+| **[`coding-dev.md`](./coding-dev.md)** | Standing rules for all code work: maximum linter/compiler strictness, never filtering build output, reuse-before-reinvent dependency ordering, file/function size limits, test & regression discipline, verification gates, scope control, commit hygiene, and honest reporting. |
+
+### 🔤 Per-Language Rules ([`code-languages/`](./code-languages/))
+
+| Language | Skill File | Highlights |
+| :--- | :--- | :--- |
+| **Rust** | [`rust.md`](./code-languages/rust.md) | `--workspace` clippy gate, `[workspace.lints]` single source of truth, no `unwrap`/`unsafe`, core-crate split |
+| **TypeScript / JavaScript** | [`js-typescript.md`](./code-languages/js-typescript.md) | TS > JSDoc > plain JS, banned constructs table, React & hooks rules, resource lifecycle, sandbox boundaries |
+| **Bash / Shell** | [`bash.md`](./code-languages/bash.md) | `set -euo pipefail`, shellcheck, no wait loops, destructive-command guards, build-gate structure |
+| **Python** | [`python.md`](./code-languages/python.md) | `mypy --strict`, broad ruff rule set, asyncio task discipline, rate-limit queueing |
+| **Go** | [`go.md`](./code-languages/go.md) | strict `golangci-lint` set, concrete types over `interface{}`, context everywhere, CGO-free static builds |
+| **C# / .NET** | [`csharp-dotnet.md`](./code-languages/csharp-dotnet.md) | `TreatWarningsAsErrors`, nullable enabled, no `.Result`, trimming/single-file publish caveats, SDK shims |
+| **C / C++** | [`c-cpp.md`](./code-languages/c-cpp.md) | full warning set + `-Werror`, sanitizers, RAII/Rule of Zero, target-based CMake, FFI ownership |
+
+Each language file extends `coding-dev.md` rather than repeating it. A project's own
+`AGENTS.md` / `CLAUDE.md` / `.rules` always overrides both.
+
+---
+
+## ✍️ Skill Document Conventions
+
+Skills in this repo follow the same structure as the private counterpart repo, so agents can load either interchangeably:
+
+1. **YAML frontmatter** with `name` (kebab-case, matching the filename) and a `description` starting with *"Use this skill when …"* — the description is what an agent matches against to decide relevance, so it must enumerate concrete triggers.
+2. **Numbered `##` sections**, sequential and unique, ending with a **Related Skills** section that cross-links sibling documents.
+3. **CLI discovery over enumeration** — document the *non-obvious* workflows, gotchas, and constraints. For the routine surface, point at `<tool> --help` rather than transcribing flag lists that will go stale.
+4. **No secrets inline** — reference the environment file that holds them (e.g. `~/.config/environment.d/…`), never the values themselves.
+5. **Verify before documenting** — confirm hostnames, container names, and versions against the live system rather than carrying forward stale claims.
 
 ---