fix(tooling): mise min_version floor predates the monorepo_root key (unknown-field warning)

[scottschreckengaust]

Summary

mise.toml declares min_version = "2026.2.6", but PR #874 renamed the monorepo key from experimental_monorepo_root to monorepo_root. That key did not exist until the 2026.7.9 tag (jdx/mise#11052, 2026-07-16). Any contributor on 2026.2.6 ≤ mise < 2026.7.11 therefore gets, on every shell prompt / task run:

mise WARN  unknown field in .../mise.toml: monorepo_root

The floor no longer matches the config the repo actually requires.

Fix

Bump the floor to the first installable version that recognizes the key:

min_version = "2026.7.11"

The key first appears in the 2026.7.9 tag, but 2026.7.8–2026.7.10 were tagged and never published to the release/install channels (upstream release-pipeline issue); their changes shipped in 2026.7.11 (published 2026-07-20). Pinning to 2026.7.9 would trade a warning for an unsatisfiable requirement, so 2026.7.11 is the correct floor.

This turns a silent per-prompt warning into a clear "please upgrade mise" gate.

Acceptance

• min_version = "2026.7.11" in mise.toml.
• mise ≥ 2026.7.11 parses mise.toml with no unknown field warning.