fix(backup): Add the site name to streamed backup file names (backport #613)

[mergify]

Streamed backups were named <timestamp>-%stream%-<type> locally and <timestamp>-stream-<type> in S3, so, unlike regular backups, nothing in the object or downloaded file name said which site it belongs to.

This adds frappe's site slug (the site name with dots turned into underscores, as regular backups use), keeping the stream label:

• Local FIFO: 20260929_101500-my_site_test-%stream%-database.sql.gz
• S3 object: 20260929_101500-my_site_test-stream-database.sql.gz

The slug goes before the %stream% marker on purpose. Frappe finds recent backups with the glob *-<slug>-database.sql.gz, and a name ending in -<slug>-database.sql.gz would match a live FIFO, which blocks when opened.

Still working:

• bypass_unlink.so matches %stream% anywhere in the path (strstr), so the FIFOs keep their protection.
• The %stream%- → stream- swap for S3 keys and the pkill -f <timestamp> cleanup don't change.
• Nothing in press parses these names.

🤖 Generated with Claude Code

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This is an automatic backport of pull request #613 done by Mergify.

[mergify]

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