Revamp governance docs and README to reflect current project structure and roles

## Context

While reviewing #1009 (adding a `MAINTAINERS.md` as part of the FINOS-wide standardization effort), we noted that the project's governance documentation and README have drifted from how the project actually operates today. This issue tracks the revamp, as discussed in [this thread](https://github.com/finos/common-cloud-controls/pull/1009#discussion_r3520315114).

Historically, CCC has avoided the term "maintainer" in favor of roles like "WG Lead" and "Steering Committee Member." FINOS now requires all projects to publish a maintainer list, so we need to adopt the term — at minimum in `MAINTAINERS.md` — while keeping the role structure that works for this project. The governance docs should explain how the two fit together rather than leaving them side by side unreconciled.

## Work items

### README.md

- [ ] Reconcile the working group list with the groups that are actually active — the README states the project is "split into 6 working groups" but lists only four, while `docs/governance/working-groups/` contains eight charters (CFI, Communications, Community Structure, Delivery, Duplication Reduction, Security, Taxonomy, Website).
- [ ] Update the working group meeting table (missing groups, no chair listed for Communications; meeting cadences need verification).
- [ ] Review the Steering Committee membership table — this is the canonical record referenced by `docs/governance/community-structure.md`.

### docs/governance/

- [ ] Review `community-structure.md`, `member-roles.md`, and the WG charters for accuracy against current practice.
- [ ] Define what "maintainer" means for CCC and which existing roles confer it (e.g. WG Leads and/or SC members), so `MAINTAINERS.md` has clear criteria for who is on the list and how people are added or removed. The intent is a light touch: satisfy the FINOS requirement without renaming the roles the community already uses.
- [ ] Archive or mark inactive any working group charters that no longer have an active group.

### Website

- [ ] Align repo docs with the newer website material where appropriate — the website content may already be ahead of the repo docs in places, and Scott Logic folks working on the website (cc @gbalysevaite) have offered to review the content.

## Reference

Current technical contributors, as presented to the FINOS TOC ([finos/technical-oversight-committee#296](https://github.com/finos/technical-oversight-committee/pull/296)):

- Eddie Knight (Revanite)
- Rob Moffat (FINOS)
- Sonali Mendis (Scott Logic)
- Stevie Shiells (Scott Logic)
- Michael Lysaght (Citi)
- Leroy Abhikui (LSEG)
- Dave Reeve (Morgan Stanley)
- Jenn Power (Red Hat)
- Maxime Coquerel (RBC)
- Sankara Ramakrishnan (BlackRock)

cc @sshiells-scottlogic @aric-rosenbaum