docs: create blog post covering Gaze multi-language support

[jflowers]

Context

PR #258 adds documentation for Gaze's multi-language support via external analyzers. A companion blog post would help communicate this capability to a broader audience.

What to cover

• Why multi-language support matters for Gaze's mission
• How the external analyzer protocol works (JSON-RPC 2.0)
• The three-tier analyzer discovery mechanism
• Universal side effect types and language-neutral aliases
• How to build an external analyzer for a new language

Related

• PR docs: update Gaze documentation for multi-language support #258: docs: update Gaze documentation for multi-language support
• Closes docs: gaze multi-language support — external analyzer protocol and new CLI flags #227, docs: gaze breaking JSON change — go_version renamed to language_version #228, docs: gaze expanded side effect taxonomy — 10 new universal types #229, docs: gaze --test-short flag and coverage behavior change #230 (upstream issues addressed by PR docs: update Gaze documentation for multi-language support #258)
• gaze#180: Language-neutral aliases
• gaze#184: Universal side effect types
• gaze#194: Coverage behavior change