fix: mobile sidebar, complete version diff, and sidebar reopen

[Sathvik-Rao]

Summary

Three UI fixes:

• Mobile: the drawer was sized from --sw, which the desktop resize logic
  clamps to its 200px minimum on phone widths; combined with row action
  buttons that reserve ~90px even while hidden, the session-title column
  collapsed to 27px ("Se..."). Use a fixed min(86vw,330px) drawer width and
  reveal row actions on touch so titles are readable and favorite/rename/
  delete are reachable.
• Diff: _buildDiffHtml only compared summary, competencies, experience,
  skills, and scores, so newly added sections (projects, education, certs,
  open source, publications, patents, awards, volunteer, languages,
  interests, contact) never appeared. Add serializers for every section;
  added entries render as additions, removed as deletions, edits keep
  word-level highlighting. Experience now walks the longer job list so
  added/removed jobs show too.
• Sidebar: the expand button lived inside #sb, which is width:0;
  overflow:hidden when collapsed, so it was clipped and unclickable — no way
  to reopen. Move it into the toolbar and restyle it.

Type of change

• fix: ... — bug fix → patch bump (0.0.x)
• feat: ... — new feature → minor bump (0.x.0)
• feat!: ... / BREAKING CHANGE — breaking change → major bump (x.0.0)
• chore: / docs: / ci: / refactor: — no release created

PR title format

Your PR title becomes the commit message on merge and determines the version bump:

feat(resume): add cover letter section
fix: pdf export crash on empty work history
feat!: replace /generate endpoint with /build (breaking)
chore: update dev dependencies

Pattern: type(optional-scope): short description in lowercase

Checklist

• Tests added / updated under backend/tests/ for any changed backend/app/ code
• pytest passes locally (cd backend && pytest)
• PR title follows the format above

[github-actions]

Suggested tests for this PR

PR title: fix(frontend): mobile sidebar, complete version diff, and sidebar reopen

PR description:

Summary

Three UI fixes:

• Mobile: the drawer was sized from --sw, which the desktop resize logic
  clamps to its 200px minimum on phone widths; combined with row action
  buttons that reserve ~90px even while hidden, the session-title column
  collapsed to 27px ("Se..."). Use a fixed min(86vw,330px) drawer width and
  reveal row actions on touch so titles are readable and favorite/rename/
  delete are reachable.
• Diff: _buildDiffHtml only compared summary, competencies, experience,
  skills, and scores, so newly added sections (projects, education, certs,
  open source, publications, patents, awards, volunteer, languages,
  interests, contact) never appeared. Add serializers for every section;
  added entries render as additions, removed as deletions, edits keep
  word-level highlighting. Experience now walks the longer job list so
  added/removed jobs show too.
• Sidebar: the expand button lived inside #sb, which is width:0;
  overflow:hidden when collapsed, so it was clipped and unclickable — no way
  to reopen. Move it into the toolbar and restyle it.

Type of change

• fix: ... — bug fix → patch bump (0.0.x)
• feat: ... — new feature → minor bump (0.x.0)
• feat!: ... / BREAKING CHANGE — breaking change → major bump (x.0.0)
• chore: / docs: / ci: / refactor: — no release created

PR title format

Your PR title becomes the commit message on merge and determines the version bump:

feat(resume): add cover letter section
fix: pdf export crash on empty work history
feat!: replace /generate endpoint with /build (breaking)
chore: update dev dependencies

Pattern: type(optional-scope): short description in lowercase

Checklist

• Tests added / updated under backend/tests/ for any changed backend/app/ code
• pytest passes locally (cd backend && pytest)
• PR title follows the format above

No backend/app/**.py files changed — no test suggestions.