fix(devops): enforce graph count limit

[dajiaohuang]

What type of PR is this?

fix

Check the PR title.

• This PR title matches the format: <type>(optional scope): <description>
• The description is user-oriented and clear.
• No user documentation update is required; this restores the existing advertised limit.

(Optional) Translate the PR title into Chinese.

fix(devops): 强制执行图数量上限

(Optional) More detailed description for this PR(en: English/zh: Chinese).

en:

AddGraphInfo checked the pre-increment root graph counter with >, so it accepted 101 graphs when maxGraphNum is 100 and rejected only the 102nd call. This changes the boundary check to >= and adds a regression test verifying that the 101st graph is rejected without mutating the counter or container.

Validation:

• go test -gcflags='all=-N -l' ./internal/service -run '^Test_containerServiceImpl_AddGraphInfo$' -count=1 (Windows, Go 1.26.3)
• go test -race -gcflags='all=-N -l' ./internal/service -run '^Test_containerServiceImpl_AddGraphInfo$' -count=1 (Linux, Go 1.25.6)
• go vet ./internal/service
• git diff --check

(Optional) Which issue(s) this PR fixes:

Fixes #960

(optional) The PR that updates user documentation:

Not required.