Align the "Application" document-metadata value across all deployments (drop leftover ONLYOFFICE)

[chrip]

Problem

Saved documents carry an Application property (docProps/app.xml and the equivalent
field for other formats), written by the native converter (x2t) verbatim from the
APPLICATION_NAME env var. That var is set independently per deployment method, so the
value a user sees depends on how DS was installed — and some paths can still emit the old
ONLYOFFICE brand.

Follow-up from #274 (fixed the Docker standalone configs). Related: #273.

Current values (verified in-tree)

Deployment	Source	Value
Docker standalone	build/configs/standalone/supervisor/ds-*.conf:5 (after #274)	euro-office
Docker orchestrated	build/.docker/orchestrated.bake.Dockerfile:9,12 (COMPANY_NAME_LOW)	euro-office
systemd / RPM	document-server-package/common/documentserver/systemd/ds-*.service.m4:12 ← Makefile COMPANY_NAME ?= EURO-OFFICE (Makefile:5,283)	EURO-OFFICE
Windows	document-server-package/exe/winsw/*.xml:16 ← {#sCompanyName}	in-repo default ONLYOFFICE (exe/defines.iss:3), overridden by BRANDING_DIR\defines.iss — needs verification against the Euro-Office brand
x2t fallback (env unset)	core/DesktopEditor/common/SystemUtils.h:38-40	ONLYOFFICE unless APPLICATION_NAME_DEFAULT is defined at compile time

Goals (priority order)

1. Replace every remaining ONLYOFFICE / onlyoffice with the new brand in this field — no document should ship with the old name. Primary suspects: the Windows branding defines.iss (sCompanyName) and the x2t compile-time default (APPLICATION_NAME_DEFAULT).
2. Converge on one canonical value + casing across all deployments. Decide between euro-office (lowercase slug, current Docker value) and a properly-cased brand (Euro-Office / EURO-OFFICE), then apply it everywhere.
3. Ideally derive APPLICATION_NAME from a single source of truth so it can't drift again — today docker-bake defaults COMPANY_NAME="Euro-Office" (→ lowercased to euro-office) while the package Makefile defaults COMPANY_NAME ?= EURO-OFFICE, which is the root of the split.

Acceptance criteria

• A document created by each deployment (Docker standalone, Docker orchestrated, systemd/RPM, Windows) shows the same Application value.
• That value is the new brand — no ONLYOFFICE anywhere, including the x2t fallback when the env var is unset.

Source locations to touch

• build/configs/standalone/supervisor/ds-{adminpanel,converter,docservice,example}.conf (line 5)
• build/.docker/orchestrated.bake.Dockerfile — COMPANY_NAME_LOW (l.9) / APPLICATION_NAME (l.12)
• document-server-package/Makefile — COMPANY_NAME (l.5 & l.283)
• document-server-package/common/documentserver/systemd/ds-{docservice,adminpanel,converter}.service.m4 (line 12)
• document-server-package/exe/winsw/{DocService,Converter,AdminPanel}.xml (~l.16) + the branding defines.iss (sCompanyName)
• core/DesktopEditor/common/SystemUtils.h:38-40 — compile-time default APPLICATION_NAME_DEFAULT

Refs: #273, #274

Assisted-by: ClaudeCode:claude-opus-4-8