docs: remove outdated statements from readme

[daggerok]

What changed

• Stack: Vite -> Parcel (intro, Tech Stack, dev server step)
• Features rewritten to match the code:
  • parser: quotes, escaped quotes and newlines; most common width; rows of that width plus the Fidelity trailing comma
  • "Global Interactive Dropzone" -> click-to-import (there is no drag and drop)
  • "CSS containment" and sticky left-0 columns -> sticky headers plus anchor-pinned columns (per file in tabs, shared in merge)
  • added column types, merge view and export, which existed but were not described
• Privacy notice: "completely secure" removed, states that Remember Data (default on) keeps files in localStorage until turned off or Clear Data
• Known Issues: dropped history notes (fix(csv): keep the fidelity header, signed numbers and safe settings #19 fix, single-file decision, IndexedDB note) and the README-drift part, which this PR resolves; that item is now "Unused and vulnerable dependencies"

How it was checked

• Each new statement checked against src/main.tsx: naturalCollator file sort, type badge cycle, pinnedColumns and pinnedColumnsByFile, clearPersistedDataSets on Remember Data off and Clear Data, no onDrop, no contain: in CSS
• grep -n "Vite\|completely\|PR #" README.md returns nothing, git diff --check