feat: add Anthropic provider adapter

Streaming, tool use (with InputJSONDelta assembly), thinking blocks,
cache token tracking, system prompt separation. Tool name sanitization
(fs.read → fs_read) for Anthropic's naming constraints with reverse
translation on tool call responses.

Hardcoded model list with capabilities (Opus 4, Sonnet 4, Haiku 4.5).
Wired into CLI with ANTHROPIC_API_KEY + ANTHROPICS_API_KEY env support.

Also: migrated Mistral SDK to github.com/VikingOwl91/mistral-go-sdk.

Live verified: text streaming + tool calling with claude-sonnet-4.
126 tests across 9 packages.

go.mod

@@ -2,4 +2,15 @@ module somegit.dev/Owlibou/gnoma
 
 go 1.26.1
 
-require github.com/VikingOwl91/mistral-go-sdk v1.2.1
+require (
+	github.com/VikingOwl91/mistral-go-sdk v1.2.1
+	github.com/anthropics/anthropic-sdk-go v1.29.0
+)
+
+require (
+	github.com/tidwall/gjson v1.18.0 // indirect
+	github.com/tidwall/match v1.1.1 // indirect
+	github.com/tidwall/pretty v1.2.1 // indirect
+	github.com/tidwall/sjson v1.2.5 // indirect
+	golang.org/x/sync v0.16.0 // indirect
+)