docs: context7 documentation + config (closes #7)

[gsdali]

Closes #7.

Adds context7-compliant documentation for the C API (this is a C/C++ library, not Swift) plus a root context7.json. There was previously no docs/ directory — this PR creates one.

Files

• context7.json — projectTitle: simpleOCCTVP; folders: ["docs","src"]; excludeFolders: ["build",".build","okf","tests"]; 7 rules covering shared-library linking, the cdecl ot_* / occt_templot_* calling convention, opaque handle / lifetime ownership, struct-buffer freeing, and the offscreen render entry point.
• docs/reference/c-api.md — full C API reference grouped by area (lifecycle, shape handles, shape I/O, healing & analysis, mesh extraction, offscreen render, standalone camera, display drawer). Each function has its exact C signature, description, params, return/ownership semantics, and runnable C snippets, plus a Pascal-binding example.
• docs/guides/getting-started.md — runnable C walkthrough: link the shared lib, load a shape, extract a mesh, render a PNG, with per-platform compile/link commands.

Grounding & verification

• Every documented function is a real export from src/occt_templot.h (verified against the header — zero invented APIs).
• The Pascal section reflects the actual binding in pascal/occt_templot.pas.
• context7.json is valid JSON; description is 193 chars (≤200); every rule is ≤255 chars.

Render markers (TODO)

This library does offscreen rendering, but no PNGs are produced in this PR. Each render example carries an inline <!-- 3D render TODO: example rendered PNG --> marker where a rendered image should later be embedded. No nonexistent image links were added.

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