feat(labs): experience-first landing with lab preview mockup and sidebar catalog

Redesigned the labs landing page to lead with the experience:
- Hero shows a clickable macOS-style window mockup of Lab 01 with
  the three-step flow (scenario, prediction lock, revealed chart)
- Removed card wall, featured labs, and how-it-works sections
- The mockup IS the pitch — sidebar handles the full catalog
- Added sidebar navigation with all 33 labs organized by volume/phase
- Landing page uses page-layout: custom with sidebar: false for
  clean full-bleed hero

Author: profvjreddi

labs/config/_quarto-html.yml

@@ -39,10 +39,119 @@ website:
     keyboard-shortcut: ["/"]
 
   # Shared navbar from navbar-common.yml (via metadata-files).
+  # Site-local dropdown for quick navigation within labs.
   navbar:
     logo: "assets/images/favicon.png"
     search: true
     title: "Machine Learning Systems"
+    left:
+      - text: "Labs"
+        menu:
+          - icon: lightbulb
+            text: "Labs Home"
+            href: ./index.qmd
+
+  sidebar:
+    - id: labs-sidebar
+      style: "floating"
+      background: light
+      search: true
+      collapse-level: 2
+      contents:
+        - text: "Labs Home"
+          href: index.qmd
+        - text: "---"
+        - section: "Volume I: Foundations"
+          contents:
+            - section: "I. Foundations"
+              contents:
+                - text: "00 · The Architect's Portal"
+                  href: vol1/lab_00_introduction/
+                - text: "01 · The AI Triad"
+                  href: vol1/lab_01_ml_intro/
+                - text: "02 · The Iron Law"
+                  href: vol1/lab_02_ml_systems/
+                - text: "03 · The Silent Degradation Loop"
+                  href: vol1/lab_03_ml_workflow/
+                - text: "04 · The Data Gravity Trap"
+                  href: vol1/lab_04_data_engr/
+            - section: "II. Build"
+              contents:
+                - text: "05 · The Activation Tax"
+                  href: vol1/lab_05_nn_compute/
+                - text: "06 · The Quadratic Wall"
+                  href: vol1/lab_06_nn_arch/
+                - text: "07 · The Kernel Fusion Dividend"
+                  href: vol1/lab_07_ml_frameworks/
+                - text: "08 · The Training Memory Budget"
+                  href: vol1/lab_08_model_train/
+            - section: "III. Optimize"
+              contents:
+                - text: "09 · The Data Selection Tradeoff"
+                  href: vol1/lab_09_data_selection/
+                - text: "10 · The Compression Frontier"
+                  href: vol1/lab_10_model_compress/
+                - text: "11 · The Roofline"
+                  href: vol1/lab_11_hw_accel/
+            - section: "IV. Deploy"
+              contents:
+                - text: "12 · The Speedup Ceiling"
+                  href: vol1/lab_12_perf_bench/
+                - text: "13 · The Tail Latency Trap"
+                  href: vol1/lab_13_model_serving/
+                - text: "14 · The Silent Degradation Problem"
+                  href: vol1/lab_14_ml_ops/
+            - section: "Capstone"
+              contents:
+                - text: "15 · There Is No Free Fairness"
+                  href: vol1/lab_15_responsible_engr/
+                - text: "16 · The Architect's Audit"
+                  href: vol1/lab_16_ml_conclusion/
+        - text: "---"
+        - section: "Volume II: At Scale"
+          contents:
+            - section: "I. Foundations"
+              contents:
+                - text: "01 · The Scale Illusion"
+                  href: vol2/lab_01_introduction/
+                - text: "02 · The Compute Infrastructure Wall"
+                  href: vol2/lab_02_compute_infra/
+                - text: "03 · Communication at Scale"
+                  href: vol2/lab_03_communication/
+                - text: "04 · The Data Pipeline Wall"
+                  href: vol2/lab_04_data_storage/
+            - section: "II. Build"
+              contents:
+                - text: "05 · The Parallelism Puzzle"
+                  href: vol2/lab_05_dist_train/
+                - text: "06 · When Failure Is Routine"
+                  href: vol2/lab_06_fault_tolerance/
+                - text: "07 · The Scheduling Trap"
+                  href: vol2/lab_07_fleet_orch/
+                - text: "08 · The Inference Economy"
+                  href: vol2/lab_08_inference/
+            - section: "III. Optimize"
+              contents:
+                - text: "09 · The Optimization Trap"
+                  href: vol2/lab_09_perf_engineering/
+                - text: "10 · The Edge Thermodynamics Lab"
+                  href: vol2/lab_10_edge_intelligence/
+                - text: "11 · The Silent Fleet"
+                  href: vol2/lab_11_ops_scale/
+            - section: "IV. Deploy"
+              contents:
+                - text: "12 · The Price of Privacy"
+                  href: vol2/lab_12_security_privacy/
+                - text: "13 · The Robustness Budget"
+                  href: vol2/lab_13_robust_ai/
+                - text: "14 · The Carbon Budget"
+                  href: vol2/lab_14_sustainable_ai/
+            - section: "Capstone"
+              contents:
+                - text: "15 · The Fairness Budget"
+                  href: vol2/lab_15_responsible_ai/
+                - text: "16 · The Fleet Synthesis"
+                  href: vol2/lab_16_fleet_synthesis/
 
   page-footer:
     left: |