[docs] CAMPAIGNS.md: use `quest campaign` as canonical CLI verb, `quest epic` as alias

[kunallanjewar]

Follow-up from #66 (which landed the initial docs/CAMPAIGNS.md).

The doc consistently treats quest epic as the primary CLI verb, but in code the canonical command is quest campaign and epic is the alias:

// internal/quest/epic_cmd.go:29
CLIPath:    []string{"quest", "campaign"},
CLIAliases: []string{"epic"},

The comment at epic_cmd.go:25-27 is explicit:

EpicCommand is registered as quest campaign (CLIPath) with quest epic as an alias (CLIAliases). The MCP tool name stays quest_epic for backward compat.

Users following the docs end up using the alias instead of the canonical verb.

Acceptance

In docs/CAMPAIGNS.md:

• The bash example at line 69 should be guild quest campaign <campaign-name> QUEST-1 QUEST-2 ... (with a parenthetical that quest epic works as an alias).
• Prose mentions of the rename verb (lines 60, 72-73, 84) should lead with quest campaign and treat quest epic as the alias, mirroring the code's CLIPath / CLIAliases split.
• The MCP tool reference at line 74 (quest_epic) is correct and should stay — only the CLI verb naming needs flipping.

Out of scope

• No code changes. The CLI dual-naming itself is intentional.
• No restructuring of the doc's broader argument; just the verb naming.