Generate context files when they already exist in the LST

[kmccarp]

Background / problem

• When the build-time LST manifest includes existing .moderne/context/* files (as it does in moderne-cli 4.1.4+ after moderne-cli#3661), the recipes in this module that defer work to cycle 2 stop firing for repos that already have those files committed. The customer-facing symptom is that running UpdatePrethinkContextNoAiStarter across a multi-repo corpus generates context for some repos and silently skips others.

ExportContext.getVisitor returns the tree unchanged on cycle 1 because data tables are populated during the visitor phase of cycle 1 and read in cycle 2. ExportContext.generate also defers to cycle 2 for the same reason. The recipe contributes zero changes in cycle 1, and the only thing that historically kept it cycling was that some other recipe in the pipeline (typically GenerateCalmArchitecture's placeholder, which writes a {} file at .moderne/context/calm-architecture.json) made a cycle-1 change and kept the RecipeScheduler loop alive. Once that placeholder workaround stops firing -- because calm-architecture.json is now present in the scanner's accumulator -- the loop terminates after cycle 1 and ExportContext never runs. GenerateCalmArchitecture has the same shape: its cycle-1 placeholder only fires when the file is absent, and its visitor has a cycle != 2 early return.

Solution

Both recipes' cycle-1 visitor branches now call ctx.putMessage with an io.moderne.prethink.* key. RecipeRunCycle treats any ExecutionContext mutation from a recipe as "this recipe made a change" and, combined with the existing causesAnotherCycle override, enrolls the recipe for cycle 2. The CursorValidatingExecutionContextView allow-list requires the io.moderne. prefix. The fixes are defense-in-depth in pipelines where other recipes already trigger cycle 2, and become load-bearing when these recipes are used standalone or alongside other recipes that don't produce cycle-1 changes.

Test plan

• Regression tests added to ExportContextTest and GenerateCalmArchitectureTest that invoke Recipe.run directly with maxCycles=3, minCycles=1, matching the production CLI's RecipeScheduler.scheduleRun call. RewriteTest.rewriteRun cannot represent this scenario because it strictly enforces expectedCyclesThatMakeChanges, and the only way to set minCycles=1 through that API also asserts zero cycles make changes. Both tests fail without their respective fixes.
• Verified end-to-end on CLI 4.2.0 against a 3-repo corpus (three private moderneinc repos): per-repo .moderne/context/* entries in fix.patch go from 21 + 0 + 0 (broken) to 21 + 16 + 18 (each repo now produces output). The numeric delta vs CLI 4.1.2's 28 + 24 + 21 is byte-identical existing on-disk content (verified with a per-file diff) -- the patch is minimal-diff while the pre-#3661 codepath emits "create new file" entries even when content matches.
• Verified backward compatibility: CLI 4.1.2 against the same patched jar still produces 28 + 24 + 21.

Relationship to #17

#17 is an alternative that fixes the same bug and introduces a PrethinkContextRecipe base class, migrating ExportContext and GenerateCalmArchitecture to extend it. Either PR can ship on its own. Pick one.