Returns the group's shared post-processing rules ("Rules for all scrapers"), the per-scraper
        values their conditions may read, the document version, and a paged per-scraper report of how
        the rules apply (which outputs a scraper's own rule overrides, which choice groups it owns,
        which inputs it does not declare).

        How group rules run: after each scraper's own rules, in list order, on every scraper of the
        group (also on uploaded-file scrapers). A scraper rule writing the same outputField wins on all
        that scraper's rows; if any rule of a choice group (branchSet) is overridden, the whole choice
        group is skipped for that scraper. A rule may have up to 3 conditions (AND): op equals / in /
        contains / notBlank / blank on a row field (a row value that is not blank wins, else the
        scraper's value from scraperValues). Rules in a choice group run only when exactly ONE choice's
        conditions hold; none -> row warning RULE_NO_BRANCH:<set>, several -> RULE_MULTI_BRANCH:<set>
        (never a default). Other row warnings (in _sw_warnings): RULE_NO_INPUT:<output> (a quantityField
        or fromField is missing), RULE_UNUSABLE:<output> (divisor <= 0 or not a number, unknown
        currency, output already a scraped column). CURRENCY_CONVERT may read the source currency per
        row with params.fromField instead of a fixed params.from. It writes its outputField plus ONE
        shared pair per target currency per row: <to>_rate and <to>_rate_date (e.g. eur_rate,
        eur_rate_date), shared by every rule (scraper or group) converting to that currency; one rate
        table per run. RULE_RATE_CONFLICT:<to>_rate when two rules on one row need two different rates
        (both values kept, no pair). A row that already has its own eur_rate / eur_rate_date keeps it;
        a group CURRENCY_CONVERT to EUR then gets RULE_UNUSABLE:<output>.
        Members of ONE choice group may share an outputField (same kind and outputType, and for
        CURRENCY_CONVERT the same to): only the picked choice writes it; no or several choices -> none
        of the group's outputs is written. ENUM_MAP with an empty mapping and a default writes that
        default as a fixed value (on rows whose sourceField is not blank).

        Args:
          - id (string, path param, required): the group's MongoDB ObjectId.
          - page (int, query, optional, default 0): page of the per-scraper report.
          - size (int, query, optional, default 200, max 200): rows per page.
          - filter (string, query, optional, default ALL): ALL | OWN (scrapers with their own rule for a
            group output) | PROBLEMS (scrapers with row warnings); q (string, optional, at most 100
            characters): scraper name contains, case-insensitive; split (bool, optional): with ALL, the
            scrapers with row warnings come in problemScrapers and the page holds the others; summary
            (bool, optional): adds summary {problemLines, ownRuleScrapers}.

        Returns:
          GroupPostProcessRulesDTO — rules, scraperValues, version (0 = no rules yet), updated,
          updatedBy (the account owner's email when they made the last change, else null), counts {scrapers, overridden, missingDeclaredInput, missingValue}, scrapers
          (the page of per-scraper rows), page, size, totalScrapers.
          Each row also has missingLabels and rowWarnings [{code, choiceGroup, rows}]: rows stored with
          RULE_NO_BRANCH / RULE_MULTI_BRANCH in that scraper's latest run (counts.withRowWarnings,
          matchingScrapers = the rows behind the page after q/filter/split).

        Examples:
          - Use when: "which rules apply to every scraper in group {id}?"
          - Use when: before scrapewise_update_scraper_group_post_process_rules, to read the version
          - Don't use when: you want one scraper's own rules -> scrapewise_get_scraper

        Error Handling:
          - 400 (CustomerError envelope) if no group with this id exists for this customer (also for a
            group only shared with you), or size > 200.
          - 401 Unauthorized.
          - 500 INTERNAL.