Downgrade: raise RecipesBase compat floor to 1.0 (incompatible with Plots 1 below)

[ChrisRackauckas-Claude]

The MINIMUM-VERSION (downgrade) job fails. Reproduced locally on Julia 1.10 (the LTS downgrade floor); the conflict is:

Unsatisfiable requirements detected for package Plots [91a5bcdd]:
 Plots [91a5bcdd] log:
 ├─restricted to versions 1 by project, leaving only versions: 1.0.0-1.41.6
 └─restricted by compatibility requirements with RecipesBase [3cdcf5f2]
   to versions: 0.29.0-0.29.9 or uninstalled — no versions left
     └─RecipesBase restricted to versions 0.8.0 by an explicit requirement

Why the old floor was impossible

• At the downgrade minimum RecipesBase is pinned to its floor 0.8.0 (compat RecipesBase = "0.8, 1.0"), and the test dep Plots is pinned to its floor 1.0.0 (compat Plots = "1").
• In the registry, every Plots 1.x requires RecipesBase = "1" (Plots 1.0-1.23 -> RecipesBase 1). RecipesBase 0.8.x is only co-installable with the pre-1.0 Plots 0.29.x.
• So RecipesBase 0.8.0 and Plots 1 have an empty intersection -> Unsatisfiable. Bumping the Plots floor cannot help, since no Plots >= 1 supports RecipesBase 0.8.

Fix

Raise the lower bound: RecipesBase = "0.8, 1.0" -> RecipesBase = "1.0". 1.0 is the smallest RecipesBase co-installable with Plots 1. The @recipe API this package uses is unchanged between RecipesBase 0.8 and 1.0; no upper bound lowered, no test logic touched.

Resolve verification (local, Julia 1.10 LTS)

Mimicking julia-downgrade-compat --min (all [compat] entries pinned to their lower bounds):

• floor RecipesBase = 0.8 -> Unsatisfiable (reproduces CI).
• floor RecipesBase = 1.0 -> RESOLVE SUCCEEDED (installs Plots v1.23.6, exit 0).

Resolution only — the full test suite was not run locally; PR CI confirms.

Ignore until reviewed by @ChrisRackauckas.