docs: rewrite README and CONTRIBUTING for full registry scope

- README now covers all 5 content types (agents, hands, integrations, skills, providers)
- CONTRIBUTING has per-type instructions and checklists
- validate.py expanded to validate agents, hands, integrations, and skills
- PR template covers all content types
- Added new-content.yml issue template for non-model contributions
- CI workflow updated to Python 3.12

.github/pull_request_template.md

@@ -1,14 +1,52 @@
-## Model Changes
+## Content Type
 
-### Added/Updated Models
-- [ ] Model ID:
-- [ ] Provider:
-- [ ] Pricing verified from official source:
+<!-- Check all that apply -->
 
-### Checklist
+- [ ] Agent (`agents/`)
+- [ ] Hand (`hands/`)
+- [ ] Integration (`integrations/`)
+- [ ] Skill (`skills/`)
+- [ ] Provider / Model (`providers/`)
+- [ ] Other
+
+## Changes
+
+### Added/Updated
+-
+
+### Details
+<!-- Brief description of what was added or changed -->
+
+## Checklist
+
+### General
+- [ ] Content placed in the correct directory
+- [ ] TOML files parse without errors
+- [ ] Description is clear and concise
+
+### Providers / Models (if applicable)
 - [ ] `python scripts/validate.py` passes
 - [ ] No duplicate model IDs
-- [ ] Pricing is in USD per million tokens
+- [ ] Pricing is in USD per million tokens and verified from official source
 - [ ] Tier is one of: `frontier`, `smart`, `balanced`, `fast`, `local`
-- [ ] `context_window` and `max_output_tokens` are positive integers
-- [ ] Boolean fields (`supports_tools`, `supports_vision`, `supports_streaming`) are correct
+
+### Agents (if applicable)
+- [ ] `name` matches directory name
+- [ ] System prompt provides clear instructions
+- [ ] Tools list only includes required tools
+
+### Hands (if applicable)
+- [ ] `id` matches directory name
+- [ ] `[agent]` section has complete system prompt
+- [ ] `[[requires]]` lists external dependencies
+- [ ] `[[settings]]` provides user-configurable options
+
+### Integrations (if applicable)
+- [ ] `[transport]` config tested locally
+- [ ] `[[required_env]]` lists all needed variables
+- [ ] `setup_instructions` are clear for first-time users
+
+### Skills (if applicable)
+- [ ] `[runtime].type` is correct
+- [ ] `[input]` documents all parameters
+- [ ] Prompt templates use correct `{{param}}` syntax