Site accuracy audit after the ACT4 milestone

After P26 landed, the notebook needed an honesty pass.

Audit scope:

• all project frontmatter under site/src/content/projects;
• artifact links declared in project frontmatter;
• hardened project evidence for final GDS and metrics;
• RISC-V project pages for explicit compliance caveats;
• current milestone language on the home, project index, start, and roadmap pages.

Mechanical checks:

projects=26 orders=1..26
NO_ISSUES

Fixes made:

• Added P26 to the site and agent roadmap.
• Rewrote the Roadmap page so it no longer says P15 is today’s milestone.
• Updated the home page and project index to say the current result is the ACT4/Sail rv32i/I probe.
• Updated the Start page so it no longer describes the repo as a ten-project ladder.
• Added explicit compliance caveats to P12 and P13.

The most important wording boundary is now consistent:

P26 passes ACT4-generated, Sail-backed, self-checking rv32i/I ELFs, but this is still not a full RISC-V compliance claim.