docs: sync docs tree from main

[yicheng47]

Brings main's docs into the gpui line so port guides stop living behind git show — only docs/ is touched.

• Adopts main's impl docs 0033–0045 + archived 0032, and 0024's update — the M3 port guides, now in-tree.
• Adopts main's feature-spec layout: specs 05/19/21/24/37 move back out of archive/ (they were frozen-archived at the 2026-07-19 repo split; main's layout is canonical), plus specs 45–61 and archived 43–55 arrive.
• Three-way merges (base = fork point d9483ca) for the two dual-edited files: docs/arch/arch.md (main's superset paragraph wins — includes qoder/trae resume behavior) and docs/features/README.md (main's live index wins; one parity-only breadcrumb line added pointing at the program plan).
• docs/product/vision.md takes main's update; docs/impls/gpui-rewrite/ untouched.

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