feat: initial model catalog with 196 models across 39 providers

Community-maintained TOML catalog for LibreFang. New models can be added
via PR without requiring a LibreFang binary release.

Includes validation script, bilingual docs, and GitHub templates.

.github/ISSUE_TEMPLATE/new-model.yml

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+name: New Model Request
+description: Request addition of a new AI model to the catalog
+labels: ["new-model"]
+body:
+  - type: input
+    id: model_id
+    attributes:
+      label: Model ID
+      description: The canonical model identifier used by the provider's API.
+      placeholder: e.g. gpt-5.5
+    validations:
+      required: true
+
+  - type: input
+    id: provider
+    attributes:
+      label: Provider
+      description: Which provider offers this model?
+      placeholder: e.g. openai
+    validations:
+      required: true
+
+  - type: dropdown
+    id: tier
+    attributes:
+      label: Tier
+      description: What capability tier does this model belong to?
+      options:
+        - frontier
+        - smart
+        - balanced
+        - fast
+        - local
+    validations:
+      required: true
+
+  - type: textarea
+    id: details
+    attributes:
+      label: Model Details
+      description: |
+        Please provide the following details:
+        - Context window (tokens)
+        - Max output tokens
+        - Input cost per million tokens (USD)
+        - Output cost per million tokens (USD)
+        - Supports tool/function calling? (yes/no)
+        - Supports vision/image input? (yes/no)
+        - Supports streaming? (yes/no)
+      placeholder: |
+        Context window: 128000
+        Max output: 16384
+        Input cost: $2.50 / 1M tokens
+        Output cost: $10.00 / 1M tokens
+        Tools: yes
+        Vision: yes
+        Streaming: yes
+    validations:
+      required: true
+
+  - type: input
+    id: source_url
+    attributes:
+      label: Source URL
+      description: Link to the official pricing or documentation page.
+      placeholder: e.g. https://openai.com/pricing
+    validations:
+      required: false

.github/pull_request_template.md

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+## Model Changes
+
+### Added/Updated Models
+- [ ] Model ID:
+- [ ] Provider:
+- [ ] Pricing verified from official source:
+
+### Checklist
+- [ ] `python scripts/validate.py` passes
+- [ ] No duplicate model IDs
+- [ ] Pricing is in USD per million tokens
+- [ ] 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