feat: make the parameter compatibility mode banner actionable - #29456

Follow-up to #29171, which added the compatibility_mode:true filter and linked the templates page banner to it.

The banner told admins that classic parameters were deprecated and pitched the dynamic parameters feature list. It did not say what happens if they ignore it, how much work the fix is, or use the same words as the setting they have to change.

Changes

• Use the setting's name, parameter compatibility mode, instead of "classic parameters".
• State the consequence: the legacy parameter flow will be removed in a future release.
• State the effort: switching takes one click in the template's parameter settings.
• Count-aware primary action. With more than one affected template it opens the compatibility_mode:true filter; with exactly one it links straight to that template's parameter settings and the title names the template.
• Hide the banner when the compatibility mode filter is already applied, so the action is never a no-op that reloads the current view.
• Drop prominent. A filled warning block reads as breakage; this is a migration task that stays visible until it is done.
• Relabel the docs link from View docs to How to upgrade, deep-linked to a new section.
• Docs: add Upgrade from parameter compatibility mode with the version requirements, the toggle location, the republish/refresh step, and the revert path. Also corrected the "all existing templates may be upgraded in-place" line, which read as though nothing was required of the operator.

Screenshots

Before:

After, multiple templates:

After, a single template:

Testing

tsc and biome pass. Storybook stories are updated, including a new ClassicParameterFlowWarningHiddenWhileFiltering story, but browser-mode interaction tests could not run in my environment, so CI is their first run.

Created on behalf of @matifali