feat: 样式统一 + 月份下拉框扩展

- 品牌色统一为天机阁标准 #4A6CF7，tailwind.config 扩展完整色阶
- styles.css 新增 :root CSS 变量层（brand 色阶、语义色、圆角/阴影 token）
- 全项目 hex/Tailwind 类统一替换为 brand-* CSS 变量（115 处引用）
- border-radius/box-shadow 统一使用 token 变量
- 预留 :root[data-theme="dark"] 暗色主题变量占位
- 所有月份下拉框范围从 3 年/15 月扩展至 2020-2027（8 年 96 月）

static/modules/proposals.js

@@ -53,7 +53,7 @@ function renderProposals() {
       <button class="finance-tab${!isStandard ? ' active' : ''}" style="font-size:14px;font-weight:600" onclick="switchProposalTab('other')">其他资料</button>
     </div>
     <div class="flex justify-end">${!isStandard ? `<button class="btn btn-primary btn-sm" onclick="openProposalModal()"><i data-lucide="plus"></i>新增方案</button>` : ''}</div>
-    ${isStandard ? `<div class="flex items-start gap-2 rounded-lg bg-blue-50 border border-blue-100 px-4 py-3 text-sm text-blue-700"><i data-lucide="info" style="width:16px;height:16px;flex-shrink:0;margin-top:1px"></i><span>这是每一条 OPC 线，必须要梳理清楚的 7 份资料，项目不可以删除，只可以更新附件，请大家将最新的材料上传</span></div>` : `<div class="flex items-start gap-2 rounded-lg bg-emerald-50 border border-emerald-100 px-4 py-3 text-sm text-emerald-700"><i data-lucide="lightbulb" style="width:16px;height:16px;flex-shrink:0;margin-top:1px"></i><span>在这里新建，并且上传您希望与团队其他成员共享的资料</span></div>`}
+    ${isStandard ? `<div class="flex items-start gap-2 rounded-lg bg-brand-50 border border-brand-100 px-4 py-3 text-sm text-brand-700"><i data-lucide="info" style="width:16px;height:16px;flex-shrink:0;margin-top:1px"></i><span>这是每一条 OPC 线，必须要梳理清楚的 7 份资料，项目不可以删除，只可以更新附件，请大家将最新的材料上传</span></div>` : `<div class="flex items-start gap-2 rounded-lg bg-emerald-50 border border-emerald-100 px-4 py-3 text-sm text-emerald-700"><i data-lucide="lightbulb" style="width:16px;height:16px;flex-shrink:0;margin-top:1px"></i><span>在这里新建，并且上传您希望与团队其他成员共享的资料</span></div>`}
     ${isStandard ? renderStandardTable(standardItems) : renderOtherTable(otherItems)}
   </div>
   <div id="proposalModal" class="hidden fixed inset-0 z-50 flex items-center justify-center bg-black/40" onclick="closeProposalModal()">
@@ -126,7 +126,7 @@ window.openStandardProposalDrawer = (id) => {
     </section>
     ${followupTarget ? `<section>
       <h3 class="drawer-section-title">活动 / 跟进</h3>
-      <div class="grid gap-2">${(item.followups || []).map((f) => `<div class="activity-item"><div class="activity-icon"><i data-lucide="message-square"></i></div><div class="min-w-0 flex-1"><div class="flex justify-between gap-3 text-[12px] text-slate-500"><span>${esc(f.follower)} · ${esc(f.follow_up_method)}</span><span>${esc(f.followed_at)}</span></div><div class="mt-1 leading-5 text-slate-800 rich-content" data-html="${encodeURIComponent(f.content || '')}"></div>${f.next_action ? `<p class="mt-1 leading-5 text-blue-700">下一步：${text(f.next_action)}</p>` : ""}</div><button class="activity-delete" onclick="deleteFollowup(event, ${f.id}, 'proposals', ${item.id})" title="删除评论"><i data-lucide="trash-2"></i></button></div>`).join("")}</div>
+      <div class="grid gap-2">${(item.followups || []).map((f) => `<div class="activity-item"><div class="activity-icon"><i data-lucide="message-square"></i></div><div class="min-w-0 flex-1"><div class="flex justify-between gap-3 text-[12px] text-slate-500"><span>${esc(f.follower)} · ${esc(f.follow_up_method)}</span><span>${esc(f.followed_at)}</span></div><div class="mt-1 leading-5 text-slate-800 rich-content" data-html="${encodeURIComponent(f.content || '')}"></div>${f.next_action ? `<p class="mt-1 leading-5 text-brand-700">下一步：${text(f.next_action)}</p>` : ""}</div><button class="activity-delete" onclick="deleteFollowup(event, ${f.id}, 'proposals', ${item.id})" title="删除评论"><i data-lucide="trash-2"></i></button></div>`).join("")}</div>
       <form class="comment-box mt-3" onsubmit="submitStandardComment(event, ${item.id})">
         <div class="squire-toolbar">
           <button type="button" class="squire-btn" onmousedown="event.preventDefault();squireCmd('bold')" title="加粗"><i data-lucide="bold"></i></button>