fix(cli): comma-split network-bans and network-restrictions slice flags like pflag (CLI-1983)

[Coly010]

What changed

Go declares both --db-unban-ip (network-bans remove, cmd/bans.go:48) and --db-allow-cidr (network-restrictions update, cmd/restrictions.go:40) with pflag's StringSliceVar, which CSV-splits every occurrence (--db-unban-ip=1.2.3.4,5.6.7.8 → two IPs) and appends across repeated flags. The TS legacy ports used plain Flag.string(...).pipe(Flag.atLeast(0)) with no splitting, so a comma-separated value stayed one token and failed validation (invalid IP address: 1.2.3.4,5.6.7.8 / failed to parse IP: 1.2.3.0/24,5.6.7.0/24) where the Go CLI accepts both values.

Both flags now route through the existing parity-reviewed legacyParseStringSliceFlag helper (the same encoding/csv-faithful pipeline already used by sso --domains, postgres-config --config, start, and status), using the established Flag.mapTryCatch pattern. This restores Go-identical semantics: comma-split per occurrence, append across repeats, CSV quoting for embedded commas, no trimming, and parse-time rejection of malformed CSV (which, as in Go, precedes the --experimental gate and handler validation).

Scope check: these are the only two StringSliceVar flags in either command family (--bypass-cidr-checks and --append are booleans, --project-ref is a plain string), so no sibling flags needed the same fix. Flag names, defaults, and help text are unchanged, so docs/go-cli-porting-status.md needs no update.

New coverage: flag-parse unit tests per command (comma split, quoted embedded comma, unset default, malformed-CSV rejection) plus integration scenarios that run the real flag pipeline into the handler and assert the resulting request bodies (comma form, repeated append, mixed, single-value regression, and an invalid post-split element failing before any API call). The new tests fail without the fix.

Review notes (deliberately left open)

• The rendered flag-error wording for malformed CSV (Go's invalid argument "..." for "--db-unban-ip" flag: parse error ... wrapper) is asserted nowhere in the repo — a pre-existing gap shared with the sso/postgres-config slice-flag tests; this PR matches the existing pattern rather than solving it unilaterally.
• In the pathological double-error case (-o bad plus malformed CSV in one invocation), TS surfaces the CSV parse error while Go's winner depends on argv order; both exit non-zero. No action taken.

Fixes CLI-1983
https://linear.app/supabase/issue/CLI-1983/db-unban-ip-and-db-allow-cidr-dont-comma-split-like-gos-stringslicevar

[Coly010]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🚀

Reviewed commit: 09ab038073

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