chore(adr): adopt ADR-0108 deep-dive deliverables rule (closes #38)

[lusoris]

Summary

• Adopts the six deep-dive deliverables rule (ADR-0108) for every fork-local PR — research digest, decision matrix in the ADR, AGENTS.md invariant note, reproducer command, CHANGELOG.md "lusoris fork" entry, and rebase note.
• Three project-fit adaptations from the sister-repo policy (per user direction):
  • Naming: cauda → lusoris / fork everywhere (and on issue chore: adopt 'deep-dive deliverables' rule — document lusoris-fork-local deltas on top of upstream #38 itself), matching this fork's existing naming (versioning, copyright, branch names).
  • Changelog: reuse the existing CHANGELOG.md "lusoris fork" section rather than a separate CHANGELOG-cauda.md.
  • Trigger scope: any fork-local PR (not only feature-like changes), with the existing backlog backfilled in this same PR.
• New scaffolding: docs/research/ (digest tree + template + empty index), docs/rebase-notes.md (10 grouped workstream entries backfilled — SIMD double-precision accumulation, CUDA ADM decouple-inline, SYCL pool/D3D11/picture-pool, DNN runtime, --precision flag, Netflix golden gate, build pins, workspace relocations, license headers, .claude/ agent tree).
• PR template grows a new "Deep-dive deliverables (ADR-0108)" section with the six checkboxes and a Reproducer code block.
• CLAUDE.md §12 gets rule 11; AGENTS.md §12 gets rule 9 (mirror); ADR README index gains the row for ADR-0108.

Closes

Closes #38.

Deep-dive deliverables (ADR-0108) — for this PR

• Research digest — no digest needed: trivial — this PR is the rule's adoption; the rationale lives in ADR-0108's ## Context and ## Alternatives considered.
• Decision matrix — docs/adr/0108-deep-dive-deliverables-rule.md ## Alternatives considered (5 rows: verbatim port, feature-like-only, no-rule, mega-doc, no-backfill).
• AGENTS.md invariant note — no rebase-sensitive invariants beyond the rule itself, which is captured by ADR-0108 + CLAUDE.md/AGENTS.md updates.
• Reproducer / smoke-test command — see Reproducer below.
• CHANGELOG.md "lusoris fork" entry — ### Changed → "Engineering process".
• Rebase note — docs/rebase-notes.md entry 0010 (".claude/ agent scaffolding + ADR tree + AGENTS.md / CLAUDE.md") covers the policy-tree itself; the nine workstream backfills also land in this PR.

Reproducer

```bash

1. Confirm ADR-0108 + scaffolding render in mkdocs without broken links

mkdocs build --strict

2. Confirm the new ADR file is indexed

grep -n "ADR-0108" docs/adr/README.md

3. Confirm the PR template now carries the six-deliverable section

grep -n "Deep-dive deliverables" .github/PULL_REQUEST_TEMPLATE.md
```

Test plan

• CI: docs-only change — confirm mkdocs strict build, link check, and lint jobs are green.
• Manual: open docs/adr/0108-deep-dive-deliverables-rule.md — Status, Date, Deciders, Tags, References present; body reads as neutral English.
• Manual: open docs/rebase-notes.md — 10 workstream entries with consistent format; ADR cross-links resolve.
• Manual: open .github/PULL_REQUEST_TEMPLATE.md — six-deliverable section + Reproducer code block render correctly.
• Manual: confirm CLAUDE.md §12 and AGENTS.md §12 carry the new rule.
• Manual: re-read issue chore: adopt 'deep-dive deliverables' rule — document lusoris-fork-local deltas on top of upstream #38 on GitHub — body uses lusoris / fork, not cauda.

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