docs: add spec, plan, and tasks for filters task wording fix (#12)

specs/012-filters-tasks/spec.md

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+# fix: rewrite CSS Filters tasks to describe visual outcomes instead of exact code
+
+**Issue:** [#12](https://git.librete.ch/libretech/code-crispies/issues/12)
+**Repository:** libretech/code-crispies
+**Author:** libretech
+**State:** open
+**Labels:** none
+
+## Problem
+
+Pedagogy audit: the Filters module has a 100% copy-paste score. Every exercise gives the exact CSS declaration in the task text, so students can complete lessons without understanding the concepts.
+
+## Requirements
+
+- Rewrite ONLY the filters module (`lessons/11-filters.json`) task descriptions to describe the desired visual effect instead of the exact code
+- Accept multiple valid values in validations (e.g., accept blur values between 2px and 8px instead of only 4px)
+- Do NOT change any other module
+
+## Example
+
+- **Before:** "Add `filter: blur(4px)`"
+- **After:** "Blur the background image to create a frosted-glass effect. Use a blur radius between 2px and 8px."
+
+## Acceptance Criteria
+
+1. All 4 filter lesson tasks describe visual outcomes, not exact CSS
+2. Validations accept a range of valid values using regex patterns
+3. Validation messages provide pedagogical hints without revealing answers
+4. No changes to any file outside `lessons/11-filters.json`
+5. Existing tests continue to pass