test(project-manager): add unit test suite for ProjectManager

Add 105 tests covering all public methods of the extracted ProjectManager
class, raising statement coverage from 0% to 72.79% and clearing the
Codecov patch coverage gate (≥56.80%).

Coverage highlights
- doLoadAnimation: interval, counter wrap at 9 ticks
- _loadStart: no session, existing session, bad session key removal,
  textMsg error recovery
- _loadProject: 2500ms timeout body, textMsg error, missing planet
  methods, __functionload branch (run:true / firstRun:true)
- prepareExport: value blocks (chord, note, default), named blocks
  (start, temperament1, nopValueBlock, matrixData, wrapmode), null entry
- saveLocally: happy path, allProjects setter error, thumbnail via
  Image.onload, canvas getContext error
- _midiImportBlocks: confirm button presence, cancel removes modal
- _setupFileHandlers: click clears value, change handler (null file,
  MIDI, read error, no file selected)
- start(): single-param id URL, multi-param id URL, unknown param,
  callback scheduling; window.history.replaceState used instead of
  delete window.location (non-configurable in jsdom 26)

Signed-off-by: Vanshika <pahalvanshikaa@gmail.com>

Author: vanshika2720