feat(anthropic): add Claude Opus 4.7 and fix Opus 4.6 context window (#66)

Add `claude-opus-4-7`, Anthropic's current flagship model (per
https://platform.claude.com/docs/en/docs/about-claude/models/overview).

- Context window: 1,000,000 tokens (Opus 4.7 ships with a new tokenizer)
- Max output: 128,000 tokens
- Pricing: $5 / input MTok, $25 / output MTok (unchanged from 4.6)
- Tier: frontier
- Supports tools, vision, streaming, and adaptive thinking

Move the `opus` / `claude-opus` aliases from 4.6 to 4.7 so a user asking
for "opus" gets the current flagship. Opus 4.6 is now in Anthropic's
"Legacy" section of the models overview; keeping it in the registry
entry (for existing callers that pin the exact ID) but without the
generic aliases.

Also **correct Opus 4.6's `context_window`**: it was listed as 200,000
tokens but the official model page has shown 1M tokens since release.
That was a pre-existing bug this PR fixes in passing since it directly
affects anyone who'd have routed queries to 4.6 expecting 1M.

Add a header comment pinning the source URL and explaining the
"latest-first" ordering convention so future additions don't silently
rebind aliases to a previous-generation snapshot.

providers/anthropic.toml

@@ -1,5 +1,5 @@
 # Anthropic — https://anthropic.com
-# Models: 6
+# Models: 7
 
 [provider]
 id = "anthropic"
@@ -8,11 +8,17 @@ api_key_env = "ANTHROPIC_API_KEY"
 base_url = "https://api.anthropic.com"
 key_required = true
 
+# Source for model metadata:
+#   https://platform.claude.com/docs/en/docs/about-claude/models/overview
+# Keep entries ordered with the currently-promoted "latest" at the top so the
+# `opus` / `claude-opus` / `sonnet` / etc. aliases resolve to the current
+# flagship and not a previous-generation snapshot.
+
 [[models]]
-id = "claude-opus-4-6"
-display_name = "Claude Opus 4.6"
+id = "claude-opus-4-7"
+display_name = "Claude Opus 4.7"
 tier = "frontier"
-context_window = 200000
+context_window = 1000000
 max_output_tokens = 128000
 input_cost_per_m = 5.0
 output_cost_per_m = 25.0
@@ -22,6 +28,20 @@ supports_streaming = true
 supports_thinking = true
 aliases = ["opus", "claude-opus"]
 
+[[models]]
+id = "claude-opus-4-6"
+display_name = "Claude Opus 4.6"
+tier = "frontier"
+context_window = 1000000
+max_output_tokens = 128000
+input_cost_per_m = 5.0
+output_cost_per_m = 25.0
+supports_tools = true
+supports_vision = true
+supports_streaming = true
+supports_thinking = true
+aliases = []
+
 [[models]]
 id = "claude-sonnet-4-6"
 display_name = "Claude Sonnet 4.6"