fix(pack): handle paths containing spaces in build and dev-server

[HoodieYlya13]

I was setting the repo up to look at something in Mail and the dev server
wouldn't start. It turned out to have nothing to do with my change:
proton-pack can't run when the checkout path contains a space.

dev-server and build fail to spawn

commandWithLog hands a single string to execa.command(), which splits it on
whitespace to decide what to execute. The string is built from
require.resolve('webpack-cli/bin/cli.js'), an absolute path, so once the repo
lives somewhere with a space in it the executable path itself gets split:

syscall: 'spawn /Users/me/Dev/clients/2',
spawnargs: [ '-', 'Proton/WebClients/node_modules/webpack-cli/bin/cli.js', 'serve', ... ]

ENOENT, with nothing pointing at the real cause.

The cleanup step deletes the wrong directory

build cleans its output with the same helper:

await commandWithLog(`rm -rf ${outputPath}`);

Split the same way, rm receives a truncated prefix of the intended path. I
reproduced this in a scratch directory containing dev/ next to
dev proton/WebClients/applications/mail/dist:

• dev/ was deleted
• the dist/ it was supposed to clean was left untouched
• exit code 0, no output, because -f suppresses the error

So it removes something unrelated and silently skips its actual job. Whether it
destroys anything depends on the truncated prefix happening to exist, which
isn't a comfortable thing to leave to chance.

validate.sh reports healthy files as empty

With the spawn issue fixed, build still failed. detectEmpty iterates an
unquoted command substitution:

for file in $(echo "$OUTPUT_FILES" | grep -E "\.$1$"); do

bash word-splits each path on spaces, [ ! -s "$file" ] is true for every
fragment, and real chunks get reported as empty:

[error] empty file: Proton/Proton-WebClients/applications/mail/dist/assets/static/6127.a83bf143.chunk.js.map

Changes

• protonPack.js: use execa's array form for the calls containing resolved
  paths, so arguments are passed as argv and never re-parsed. getWebpackArgs
  returns an array instead of a joined string, and the resolved CLI runs through
  process.execPath so it doesn't depend on the file's exec bit.
  commandWithLog is kept for the tar call, which needs shell: true for the
  glob.
• validate.sh: read the file list line by line instead of iterating an
  unquoted substitution. Also switched ((total++)) to total=$((total + 1)),
  since the former returns exit 1 on the first increment and the script runs
  under set -e.

Testing

From a path containing a space: yarn workspace proton-mail start serves the
app, and yarn workspace proton-mail build:web completes (1086 files in
dist, 35M bundle) where both previously failed. The rm -rf behaviour above
was checked in a scratch directory, before and after.