doc: B8 — Build profiles page

[NikolaRHristov]

Summary

Adds Source/Content/doc/profiles.md — the B8 (Profiles) cross-cutting concept page from the Atlas backfill plan in .claude/plans/WEBSITE-PLAN.md.

This is the prescribed first batch (1 h effort, simplest page) that establishes shared vocabulary (debug, debug-mountain, debug-electron) referenced by every later doc page.

Content

• Intro + anchor paragraph (traced to research.md §49)
• Profile matrix table (3 profiles × 5 dimensions)
• "Where this lives" code-path table (4 entries)
• Cross-link footer → architecture-processes, build-pipeline

Validation checklist

• Anchor paragraph traces to exactly one research §
• First table is verbatim from WEBSITE-PLAN.md
• "Where this lives" table has 4 file paths (≥3 required)
• Cross-link footer has 2 entries (minimum met)
• No shadow-*, dark:*, rounded-{sm,md,lg,xl}, bg-gradient-*, backdrop-blur (markdown only, no CSS)

What's next (Batch 2)

architecture-processes.md (B1) — the shared kernel that all other pages reference.