Adds inline pointers from ADR-007 (storage) to the v0.1 technical
persistence + file-layout sections, from ADR-008 (power) to the v0.1
out-of-scope and roadmap v0.8, and from ADR-009 (keyboard) to spike 4
in the v0.1 technical bring-up order.
Adds a "Related docs" header at the top of adr.md and inline "See also"
pointers from ADR-001 (binary/build tradeoffs → qfd §7) and ADR-002
(render module → v0.1 technical, top H1/H2 functions → qfd §3). Makes
the design-doc set walkable instead of a flat list.
Prior text said "~40 KB of stack space"; the v0.1 technical design's
task table sums to 76 KB (usb 8 + wifi 8 + ui 16 + render 12 + git 32).
Also widens the std::thread stack-cost note from a flat 8 KB to 8–32 KB
to match the per-task budget. No design change — 76 KB still fits
comfortably in the ESP32-S3's 512 KB internal SRAM.
