feat(r): extract R with tree-sitter and resolve calls corpus-wide - #2393

Graphify reviewed this change.

Looks safe to merge — no coupling regressions and no blocking issues, checked against the code graph (not a self-assessment).

Graphify review — findings

This PR adds R language extraction support to graphify. It introduces a new bespoke extractor (graphify/extractors/r.py) that handles R's assignment-based function definitions (<-/=/<<-/right-assign), lambdas, imports (library/require/pkg::fn), and source() calls, plus a companion r_resolution module that resolves calls corpus-wide against a shared namespace rather than per-file. It wires the extractor into the dispatch tables (.r/.R extensions and the Rscript shebang), registers the R resolver, adds an [r] optional extra, and updates the existing no-AST-extractor warning comments since R is no longer the example of an unsupported-but-counted language. The changeset also touches the changelog and a broad set of test files covering extraction, R resolution, and related behavior. I'm only describing intent and surface area; I haven't assessed whether the extraction/resolution logic is correct.

No blocking issues surfaced. 3 lower-confidence candidates did not survive cross-model review.