feat: initial text-readability-score v0.1.0 (text.readability_score@0.1.0)

Composite readability/complexity score: Flesch-DE + Verweistiefe
+ verb-distance. Reuse-lens: any project that needs to flag
"this text is hard to read" — government letters, AGB, scientific
abstracts.

Flesch-DE follows the Amstad adaptation:

  FRE_de = 180 − ASL − (58.5 × ASW)

ASL = avg sentence length (words); ASW = avg syllables per word.
A FRE_de around 30 reads as "schwer"; below 10 is technical-jargon
territory.

Verweistiefe uses an optional graph input (output of
graph.citation_extract). i.V.m.-edges count double because they
force the reader to chase a second norm.

composite_frust scales both to 0..10 and averages, so the output
is a single number the heatmap can plot against the §6 Studie
"Frust"-Achse.

Pure in-WASM, zero filesystem, zero network.

Reserved for next versions:

  - 0.2: noun-density and Schachtelsatz penalty
  - 0.3: per-paragraph breakdown so the UI can highlight the
         most-frustrating Absatz

Signed-off-by: flemming-it <sf@flemming.it>

.gitignore

@@ -0,0 +1,3 @@
+target/
+**/*.rs.bk
+.DS_Store