fix(config): treat positional file root as deploy target, not config file

[tcerqueira]

What

deno deploy --org o --app a --prod main.ts failed with Failed deserializing config file '.../main.ts'.: Unexpected word on line 1 column 1 because the positional [root-path] was passed into config discovery as a config file whenever it pointed at a file.

Why

resolve_config (rs_lib) treated any file path as WorkspaceDiscoverStart::ConfigFile. That is correct for --config deno-staging.json but wrong for a positional entrypoint/root like main.ts, which should be a deploy target.

Approach

• rs_lib: thread a from_config flag. A positional file root now discovers config from its parent directory (Paths) and includes the file in the collected manifest; only --config <file> keeps ConfigFile discovery, so non-standard config filenames still work unchanged.
• config.ts: pass fromConfig = Boolean(maybeConfigPath).
• command actions (deploy/mod.ts, deploy/create/mod.ts): normalize a positional file argument to its containing directory via a new deployRootDir helper, so the publish manifest (relative(rootPath, …)) and framework detection operate on the project directory rather than the single file — otherwise the now-reachable upload path would produce corrupted manifest keys.

Rejected alternative

Normalizing the positional file to its directory purely in TS before calling resolve_config would also suppress the error without a Rust change, but it leaves resolve_config's "any file = config file" contract implicit/fragile. Making the distinction explicit in Rust keeps that function correct for any caller.

Tests

• New Rust unit tests in rs_lib/src/lib.rs: positional_file_root_discovers_parent_config (positional main.ts → parent deno.json, file collected, no deserialize error) and explicit_config_flag_uses_named_config_file (--config deno-staging.json still uses ConfigFile discovery).
• Manually verified the repro: positional entry.ts no longer errors during config resolution (proceeds to auth), and --config <non-standard>.json debug output shows is_config_file=true.

Fixes #107