fix: remove temp migrations and prepare stack to be merged (#230)

# Remove planning documents now that map infrastructure is complete

This PR removes all planning documents that were used during the map infrastructure development. The map feature is now complete and fully integrated into the codebase, making these planning documents obsolete.

Specifically:

- Removed [PLAN.md](http://PLAN.md) which tracked the map infrastructure implementation progress
- Removed PLAN_partial_completion.md which outlined failure handling strategies
- Removed PLAN_step_output.md which detailed performance optimization plans
- Removed PLAN_race_condition_testing.md which described testing approaches
- Consolidated all temporary migrations into a single clean migration

These documents served as implementation guides during development but are no longer needed now that the features have been fully implemented. The code itself now serves as the source of truth for how map steps, failure handling, and output aggregation work.

Author: jumski

.changeset/tricky-sites-stare.md renamed to .changeset/add-array-method-to-dsl.md

@@ -1,5 +1,5 @@
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-'@pgflow/dsl': patch
+'@pgflow/dsl': minor
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 Add `.map()` method to Flow DSL for defining map-type steps

.changeset/easy-bats-nail.md renamed to .changeset/add-map-method-to-dsl.md

@@ -1,5 +1,5 @@
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-'@pgflow/core': patch
+'@pgflow/core': minor
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 Add map step type infrastructure in SQL core

.changeset/yummy-geckos-marry.md renamed to .changeset/add-map-step-type-infrastructure.md

@@ -1,5 +1,5 @@
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-'@pgflow/cli': patch
+'pgflow': patch
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 Fix: Use --config instead of --import-map for Deno compilation