docs: add v5 theorem scaffold, threat model, and benchmark plan

[mdheller]

Summary

This PR lands the first live-repo slice of the TRiTRPC v5 documentation refresh on top of the current public upstream.

Included in this PR:

• v5 profile matrix
• v5 protocol threat table
• v5 benchmark and ablation plan
• v5 repository implementation package
• v5 claims ledger (markdown form)

Notes

This PR is intentionally scoped to the new v5 support/report documents that could be landed cleanly through the connector.

Follow-up work still planned:

• replace the placeholder SECURITY.md with the bounded surface policy
• tighten the top-level README.md
• tighten docs/vnext/README.md
• tighten docs/vnext/WHAT_IS_TRITRPC_VNEXT.md
• land the full v5 white paper markdown in-repo
• remove the temporary connector probe file before final merge or in the follow-up PR

Why this split

The live upstream moved while the doc refresh was being prepared. Rather than force a stale full patch, this PR lands the new theorem-supporting scaffold first so the repo has the threat model, profile matrix, benchmark plan, and implementation package in public review.

Review focus

1. Is the narrow theorem/profile language directionally correct?
2. Is the threat table scoped appropriately for public vNext docs?
3. Is the benchmark/ablation plan the right next proof burden?
4. Should the claims ledger remain public or move to an internal companion memo?

[mdheller]

@copilot please fix the checks above so we can merge

[mdheller]

@copilot Please fix failed checks

[mdheller]

@copilot Fix the failed checks

[mdheller]

@copilot fix failed checks and conflicts

[mdheller]

Follow-up landing plan after this scaffold PR:

1. Update the existing landing files:

• README.md
• SECURITY.md
• docs/vnext/README.md
• docs/vnext/WHAT_IS_TRITRPC_VNEXT.md

2. Add the in-repo long-form white paper:

• docs/vnext/whitepaper/TRiTRPC_WHITE_PAPER_V5.md

3. Decide whether the detailed claims ledger should stay public in CSV form or remain as the lighter markdown ledger already in this branch.

Why split it this way:

• PR docs: add v5 theorem scaffold, threat model, and benchmark plan #27 lands the theorem-supporting scaffold first.
• The second PR can then focus only on the public theorem wording, bounded security posture, and the in-repo white paper.
• That keeps review load lower and avoids mixing support tables with landing-page narrative changes in one giant patch.

Recommended merge order:

• merge PR docs: add v5 theorem scaffold, threat model, and benchmark plan #27
• rebase the follow-up branch on new main
• land the four existing-file edits + white paper as one docs PR

Open review question for this PR:
Should the repo keep the white paper in-tree, or should the repo keep only the theorem scaffold + links out to release artifacts?