Add immutable lexicon model runtime

[backslash-f]

Summary

• add a language-neutral, synchronous LexiconModel API for exact lemma, source-form, alias, and gloss lookup
• memory-map the versioned packed artifact with section-level initialization checks and bounds checking for every reached record
• add an explicit full-checksum verification path for CI and installed resources while keeping ordinary model open off the corpus-scan path
• add privacy-safe 📖 model open/failure diagnostics without logging paths or vocabulary content
• prepare release 0.3.0 and adopt AgentGuidelines 0.0.34

Validation

• AgentGuidelines swift-format format-and-lint passed
• swift build passed
• swift test passed: 16 tests
• AgentGuidelines consumer validation passed
• AgentGuidelines 0.0.34 subtree matches central tag exactly
• Markdown wrapping and git diff checks passed
• full German v1 artifact checksum verification passed
• full artifact smoke: model open 0.79 ms; Haus 0.23 ms; Häuser 0.11 ms; pt-BR gloss-assisted See 0.43 ms on this Mac

Boundaries

No German-specific resolution policy, persistence, UI, form-feature API, whole-corpus deserialization, or third-party dependency was added. Storage identifiers and packed offsets remain private implementation details.