feat(lang_parser): add Kotlin language support

[Corentic AI (tobiasendres-dev)]

What

Adds Kotlin (.kt/.kts) support to lang_parser, following the pattern established by PR #67.

Why

Kotlin repos currently encode to an empty RPG. lang_parser/registry.py supports exactly 7 languages, so every .kt file fails is_supported_source() and the encoder reports Total valid source files to parse: 0, producing node_count: 1, edge_count: 0. Notably, the AST dep-graph builder does understand Kotlin, which masks the problem: encodes "succeed" while the semantic graph is empty.

Implementation

• config/kotlin.py: KOTLIN_CONFIG — class_declaration covers class/interface/enum class, object_declaration maps singletons/companion objects to class units
• kotlin_parser.py: KotlinParser, mirroring go_parser.py's structure (regex + tree-sitter hybrid) for consistency with existing parsers
• registry.py / tree_sitter_backend.py: registration + tree-sitter-kotlin grammar candidate
• pyproject.toml: adds tree-sitter-kotlin>=1.1.0 alongside the other grammars

Details worth reviewing:

• Import handling accepts both import (tree-sitter-grammars fork, used by the PyPI package) and import_header (fwcd grammar) node names — known fork divergence
• Qualified calls are captured via navigation_expression (Kotlin-specific node type)
• Handles modifier combinations (data/sealed/enum/value/fun interface), companion objects, inner classes, typealiases, suspend and context-receiver functions

Testing

• Fixture exercising 22 Kotlin constructs (sealed/value/data classes, fun interfaces, companions, inner classes, typealiases, suspend/context functions): all captured, no syntax errors reported
• Regression: 166 .kt/.kts files from a real-world Spring Boot multi-module project parse without crashes or syntax errors
• Full encode of that project produces a populated graph: 462 nodes, 8 functional areas, 113 files parsed

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