fix(autofill): align file path intent extra with BasePGPActivity

[pando85]

Problem

Selecting a Password Store entry from the Android autofill UI in a browser (reproduced in Firefox)
crashed the app 100% of the time:

FATAL EXCEPTION: main
Process: app.passwordstore.pando85, PID: 13938
java.lang.IllegalArgumentException: FILE_PATH is missing
	at app.passwordstore.ui.crypto.BasePGPActivity.getFullPath
	at app.passwordstore.ui.crypto.BasePGPActivity.requireDecryptionKeysExist
	at app.passwordstore.ui.crypto.BasePGPActivity.requireKeysExist
	at app.passwordstore.ui.autofill.AutofillDecryptActivity.onStart

Root cause

AutofillDecryptActivity declared its own private constant

private const val EXTRA_FILE_PATH = "app.passwordstore.autofill.oreo.EXTRA_FILE_PATH"

and used it both to build its intents and to read the extra in onStart(). Its base class
BasePGPActivity however resolves fullPath from a different key:

val fullPath by unsafeLazy {
  requireNotNull(intent.getStringExtra(EXTRA_FILE_PATH)) { "${EXTRA_FILE_PATH} is missing" }
}

where BasePGPActivity.EXTRA_FILE_PATH == "FILE_PATH".

The mismatch was latent until a8bfc66 ("fix: recover nested GPG scope during key selection")
made requireDecryptionKeysExist() call resolveGpgIdScope(repoRoot, File(fullPath), subDir). That
was the first time fullPath was dereferenced on the autofill path, turning a silent inconsistency
into a hard crash on every autofill decrypt.

Fix

Delete the local constant and use BasePGPActivity.EXTRA_FILE_PATH at all three call sites
(onStart, makeDecryptFileIntent, makeDecryptFileIntentSender). This matches the convention
already used by every other component that talks to a BasePGPActivity subclass — DecryptActivity,
PassSecretsMapUnlockActivity, LaunchActivity, AutofillSaveActivity, PasswordStore,
PasswordItem. AutofillDecryptActivity was the sole outlier.

This fixes the root cause rather than papering over it: filePath and the base fullPath now read
the same extra, so the gpg-id scope is resolved against the real entry path.

Why not the upstream approach

Upstream avoids the crash by giving fullPath a fallback to the repository root:

intent.getStringExtra(EXTRA_FILE_PATH)
  ?: PasswordRepository.getRepositoryDirectory().absolutePath

That silently resolves the gpg-id scope against the repo root instead of the actual entry, which
would pick the wrong key for entries in nested .gpg-id scopes. Bridging the real path is correct.

Safety / regression review

• The literal "app.passwordstore.autofill.oreo.EXTRA_FILE_PATH" appeared in exactly one file — no
  AndroidManifest.xml entry, test, deep link, or keep rule depends on it.
• AutofillDecryptActivity is exported="false", and all three intent construction sites go through
  its own companion factories (AutofillFilterView, Api26AutofillResponseBuilder,
  Api30AutofillResponseBuilder). No external component can send this intent.
• Verified BasePGPActivity.repoPath (EXTRA_REPO_PATH) is not dereferenced anywhere on the
  autofill decrypt path, so the crash does not merely move to the next missing extra.
• The missing-extra case still degrades gracefully through the existing logcat(ERROR) + finish()
  guard in onStart() — no crash.
• makeDecryptFileIntent applies putExtras(forwardedExtras) before putExtra(EXTRA_FILE_PATH, …),
  so a framework-supplied extra can never shadow the path.

Testing

• Added AutofillDecryptActivityTest (Robolectric) asserting makeDecryptFileIntent carries the
  file path under BasePGPActivity.EXTRA_FILE_PATH. This fails against the old code.
• On-device reproduction on a physical handset (Nothing, 3A281JEHN02185), app
  app.passwordstore.pando85 v1.25.1: crash reproduced and captured from logcat before the fix.
• Full local CI equivalent green:
  spotlessCheck, assembleDebug, test -PslimTests, lint.

Changelog

Added an entry under [Unreleased] → Fixed.