refactor(workflows): consolidate benchmark commands

[thejustinwalsh]

Summary

• expose one contributor command vocabulary at the root: bake, dev, build, test, check, and scripts
• replace manifest aliases and hand-written command routers with one source-metadata workflow index
• discover and validate 59 specialized fixture, font, release-size, fuzz, profile, capture, and hardware-browser workflows
• remove obsolete and closed-milestone browser probes together with their wrappers
• teach contributors and agents to use pnpm scripts list, show, and run

Verification

• pnpm scripts list indexed all current workflow metadata and rejected deleted names
• pnpm scripts show benchmark:presentation and text:bake-check reported usage, prerequisites, writes, and source owners
• complete root pnpm test and pnpm check passed
• OKF v0.2 validation: 0 conformance errors, 0 producer-profile errors, 0 warnings

This is PR 2 of 3 and depends on #39.