[P3-Feature] Add resume editing/customization UI with section selection

[Ztrimus]

Problem (relates to #21)

Users cannot:

• Choose which sections to include/exclude
• Edit generated content before PDF rendering
• Pick specific bullets to keep/remove
• Reorder sections

Solution

Phase 1: Section selection

Multi-select dropdown to choose which resume sections to generate (experience, projects, skills, education, certifications, achievements).

Phase 2: Content editing

After generation, show an editable preview where users can:

• Toggle individual bullets on/off
• Edit bullet text inline
• Reorder sections
• Add custom content

Phase 3: Integration with Reactive Resume

As suggested in #21, provide JSON export compatible with Reactive Resume for advanced editing.

Related

• [Feature] Enable users to edit resume layouts, and content in the web app #21