refactor: Rename 'extended' → 'long' + add compact sidebar fonts

BREAKING CHANGE: API parameter renamed from 'extended' to 'long'

## Breaking Change: Terminology Standardization

Renamed 'extended' to 'long' across entire codebase for consistency:

**Backend (Go):**
- internal/handlers/cv.go (7 locations)
  - Migration logic to auto-convert 'extended' → 'long' cookies
  - API validation now rejects 'extended', requires 'long'
  - Toggle state logic updated
- internal/handlers/pdf_test.go (17 occurrences)
  - Test function renamed: TestExportPDF_ExtendedWithSkills → TestExportPDF_LongWithSkills
  - All test cases, parameters, and expected filenames updated
- internal/pdf/generator.go (2 comment updates)

**Frontend:**
- PDF-EXPORT-FEATURE.md (3 occurrences)
- doc/3-API.md (parameter documentation)
- doc/7-CUSTOMIZATION.md (examples updated)
- templates/partials/modals/pdf-modal.html (button text, URLs)
- static/js/main.js (migration logic)
- static/hyperscript/toggles._hs (toggle logic)
- tests/mjs/24-pdf-download-params.test.mjs (test expectations)
- tests/mjs/test-preference-migration.test.mjs (NEW)
- tests/mjs/verify-migration.test.mjs (NEW)

**PDFs Renamed:**
- cv-extended-with_skills-jamr-2025-en.pdf → cv-long-with_skills-jamr-2025-en.pdf
- cv-extended-with_skills-jamr-2025-es.pdf → cv-long-with_skills-jamr-2025-es.pdf

**Migration:** Automatic cookie migration from 'extended' → 'long' for seamless UX

## New Feature: Compact Sidebar Fonts

Reduces page count for short CV with skills from 6 → 5 pages:

**Implementation:**
- Location: internal/pdf/generator.go (lines 154-215)
- Cookie detection: `cookies["cv-length"] == "short"`
- Font reduction: 2-6% (0.94-0.98em) - very subtle
- Only activates for: `length=short` + `version=with_skills`
- Long version: Always uses full-size fonts

**Impact:**
- Page count: 6 pages → 5 pages (16.7% reduction)
- Readability: Maintained - fonts remain professional
- Design philosophy: Subtle, natural content flow

**Testing:**
- New test: TestPDFGenerator_CompactSidebarFonts
- Comprehensive coverage of cookie detection and PDF generation
- Manual verification: 5-page PDF with compact but readable fonts

**Documentation:**
- doc/LONG-PDF-GENERATION.md (NEW, 13 KB)
  - Complete feature documentation
  - Implementation details with code examples
  - Font size breakdown table
  - Testing and troubleshooting guides
  - Compact sidebar fonts section (comprehensive)

**Files Changed:**
- 11 modified (backend + frontend + docs)
- 5 new files (2 PDFs, 1 doc, 2 tests)
- 2 files renamed (PDFs)

**Tests:** All Go tests passing, API validation verified, PDF generation tested

templates/partials/modals/pdf-modal.html

@@ -95,7 +95,7 @@
                  data-cv-format="long"
                  role="radio"
                  aria-checked="false"
-                 aria-label="{{if eq .Lang "es"}}CV Extendido - 8 páginas, versión completa{{else}}Extended CV - 8 pages, full version{{end}}"
+                 aria-label="{{if eq .Lang "es"}}CV Extendido - 9 páginas, versión completa{{else}}Extended CV - 9 pages, full version{{end}}"
                  tabindex="0"
                  _="on click
                       -- Remove selected from all cards
@@ -143,12 +143,12 @@
 
                     <!-- Page count badge -->
                     <div class="thumbnail-badge">
-                        {{if eq .Lang "es"}}8 Páginas{{else}}8 Pages{{end}}
+                        {{if eq .Lang "es"}}9 Páginas{{else}}9 Pages{{end}}
                     </div>
                 </div>
 
                 <div class="pdf-option-info">
-                    <h3>{{if eq .Lang "es"}}CV Extendido (8 páginas){{else}}Extended CV (8 pages){{end}}</h3>
+                    <h3>{{if eq .Lang "es"}}CV Extendido (9 páginas){{else}}Extended CV (9 pages){{end}}</h3>
                     <p>{{if eq .Lang "es"}}Todos los detalles{{else}}All details{{end}}</p>
                 </div>
 
@@ -250,14 +250,12 @@
                 // Short CV: clean version (no skills), short length
                 url = `/export/pdf?lang=${lang}&length=short&icons=show&version=clean`;
             } else if (selectedFormat === 'long') {
-                // Long CV: with skills sidebar, extended length
-                url = `/export/pdf?lang=${lang}&length=extended&icons=show&version=with_skills`;
+                // Long CV: with skills sidebar, long length
+                url = `/export/pdf?lang=${lang}&length=long&icons=show&version=with_skills`;
             } else if (selectedFormat === 'current') {
                 // Current view: use localStorage settings
                 let currentLength = localStorage.getItem('cv-length') || 'short';
-                // Map old values to new naming convention
-                if (currentLength === 'long') currentLength = 'extended';
-                // 'short' stays as 'short' - no mapping needed
+                // 'long' and 'short' stay as-is - no mapping needed
 
                 const currentIcons = localStorage.getItem('cv-icons') || 'show';
                 const currentTheme = localStorage.getItem('cv-theme') || 'default';