feat: add AI context resolver utility and tests

[flooryyyy]

Motivation

• Provide a deterministic utility to assemble AI prompt context from a user's selection and project graph so downstream AI features get stable, relevant input.
• Enforce exclusion rules and skip blank blocks to avoid leaking unwanted nodes or empty content into prompts.
• Respect a character budget with graceful truncation so callers can request context limited to token/char constraints.

Description

• Added src/app/components/project/utils/aiContext.ts which exports resolveAiContext and related types and implements a deterministic BFS-like traversal seeded by selectedIds with adjacency targets sorted for stable ordering.
• The resolver applies excludeIds and excludeTypes, skips blocks with empty title/content, formats blocks as # Title\n\nContent when appropriate, and returns { text, orderedIds, truncated }.
• The function enforces a maxChars budget and truncates entries with an ellipsis when necessary using truncateWithEllipsis while preserving separators (\n\n by default).
• Added unit tests in src/app/components/project/utils/aiContext.test.ts that verify traversal ordering, exclusion behavior, formatting, and truncation semantics.

Testing

• Ran the focused test file with npm test -- src/app/components/project/utils/aiContext.test.ts, which passed both tests.
• The full test suite was run as part of the commit step (vitest run) and completed successfully with all tests passing (57 tests passed).

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Codex Task