docs: correct nav structure (#2282)

Author: TomCools

docs/src/modules/ROOT/nav.adoc

@@ -1,6 +1,6 @@
 * xref:introduction.adoc[leveloffset=+1]
 * xref:planning-ai-concepts.adoc[leveloffset=+1]
-* Getting Started
+* Getting started
 ** xref:quickstart/overview.adoc[leveloffset=+1]
 ** xref:quickstart/hello-world/hello-world-quickstart.adoc[leveloffset=+1]
 ** xref:quickstart/quarkus/quarkus-quickstart.adoc[leveloffset=+1]
@@ -12,7 +12,7 @@
 ** xref:using-timefold-solver/modeling-planning-problems.adoc[leveloffset=+1]
 ** xref:using-timefold-solver/running-the-solver.adoc[leveloffset=+1]
 ** xref:using-timefold-solver/benchmarking-and-tweaking.adoc[leveloffset=+1]
-* Constraints and Score
+* Constraints and score
 ** xref:constraints-and-score/overview.adoc[leveloffset=+1]
 ** xref:constraints-and-score/score-calculation.adoc[leveloffset=+1]
 ** xref:constraints-and-score/understanding-the-score.adoc[Understanding the score]
@@ -39,9 +39,9 @@
 *** xref:upgrading-timefold-solver/migration-guides/variable-listeners-to-custom-shadow-variables.adoc[leveloffset=+1]
 *** xref:upgrading-timefold-solver/migration-guides/chained-variables-to-planning-list-variable.adoc[leveloffset=+1]
 * xref:commercial-editions/commercial-editions.adoc[leveloffset=+1]
-** xref:commercial-editions/installation.adoc[leveloffset=+1]
+** xref:commercial-editions/installation.adoc[Installation]
 ** xref:commercial-editions/performance-improvements.adoc[leveloffset=+1]
-** xref:constraints-and-score/understanding-the-score.adoc[Score Analysis]
+** xref:constraints-and-score/understanding-the-score.adoc[Score analysis]
 ** xref:responding-to-change/responding-to-change.adoc#assignmentRecommendationAPI[Recommendation API]
 ** xref:optimization-algorithms/move-selector-reference.adoc#nearbySelection[Nearby selection]
 ** xref:using-timefold-solver/running-the-solver.adoc#multithreadedIncrementalSolving[Multithreaded solving]

docs/src/modules/ROOT/pages/commercial-editions/multistage-moves.adoc

@@ -1,5 +1,5 @@
 [#multistageMoves]
-= Multistage Moves
+= Multistage moves
 
 include::./_only-enterprise.adoc[]
 

docs/src/modules/ROOT/pages/commercial-editions/performance-improvements.adoc

@@ -1,4 +1,4 @@
-= Performance Improvements
+= Performance improvements
 
 Timefold Solver Enterprise brings many performance improvements. These are shortly described here.
 

docs/src/modules/ROOT/pages/planning-ai-concepts.adoc

@@ -1,4 +1,4 @@
-= PlanningAI Concepts
+= PlanningAI concepts
 :doctype: book
 :sectnums:
 :icons: font